Winit version 0.30.3

This new implementation uses:
- The NSAppearanceCustomization protocol for retrieving the appearance
  of the window, instead of using the application-wide
  `-[NSApplication effectiveAppearance]`.
- Key-Value observing for observing the `effectiveAppearance` to compute
  the `ThemeChanged` event, instead of using the undocumented
  `AppleInterfaceThemeChangedNotification` notification.

This also fixes `WindowBuilder::with_theme` not having any effect, and
the conversion between `Theme` and `NSAppearance` is made a bit more
robust.

.github/workflows/ci.yml

@@ -226,3 +226,19 @@ jobs:
         command: check
         log-level: error
         arguments: --all-features --target ${{ matrix.platform.target }}
+
+  swc:
+    name: Minimize JavaScript
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Install SWC
+        run: sudo npm i -g @swc/cli
+      - name: Run SWC
+        run: |
+          swc src/platform_impl/web/web_sys/worker.js -o src/platform_impl/web/web_sys/worker.min.js
+      - name: Check for diff
+        run: |
+          [[ -z $(git status -s) ]]

.gitignore

@@ -3,8 +3,5 @@ target/
 rls/
 .vscode/
 *~
-*.wasm
-*.ts
-*.js
 #*#
 .DS_Store

.swcrc

@@ -0,0 +1,12 @@
+{
+	"minify": true,
+	"jsc": {
+		"target": "es2022",
+		"minify": {
+			"compress": {
+				"unused": true
+			},
+			"mangle": true
+		}
+	}
+}

Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "winit"
-version = "0.30.0"
+version = "0.30.3"
 authors = [
     "The winit contributors",
     "Pierre Krieger <pierre.krieger1708@gmail.com>",
@@ -112,10 +112,12 @@ objc2 = "0.5.2"
 
 [target.'cfg(target_os = "macos")'.dependencies]
 core-graphics = "0.23.1"
+block2 = "0.5.1"
 
 [target.'cfg(target_os = "macos")'.dependencies.objc2-foundation]
 version = "0.2.2"
 features = [
+    "block2",
     "dispatch",
     "NSArray",
     "NSAttributedString",
@@ -123,6 +125,7 @@ features = [
     "NSDictionary",
     "NSDistributedNotificationCenter",
     "NSEnumerator",
+    "NSKeyValueObserving",
     "NSNotification",
     "NSObjCRuntime",
     "NSPathUtilities",
@@ -140,6 +143,7 @@ features = [
     "NSApplication",
     "NSBitmapImageRep",
     "NSButton",
+    "NSColor",
     "NSControl",
     "NSCursor",
     "NSDragging",
@@ -281,6 +285,7 @@ features = [
     'AbortController',
     'AbortSignal',
     'Blob',
+    'BlobPropertyBag',
     'console',
     'CssStyleDeclaration',
     'Document',
@@ -316,6 +321,7 @@ features = [
     'VisibilityState',
     'Window',
     'WheelEvent',
+    'Worker',
     'Url',
 ]
 

README.md

@@ -8,7 +8,7 @@
 
 ```toml
 [dependencies]
-winit = "0.30.0"
+winit = "0.30.3"
 ```
 
 ## [Documentation](https://docs.rs/winit)

examples/child_window.rs

@@ -3,75 +3,15 @@
 fn main() -> Result<(), impl std::error::Error> {
     use std::collections::HashMap;
 
-    use winit::application::ApplicationHandler;
     use winit::dpi::{LogicalPosition, LogicalSize, Position};
-    use winit::event::{ElementState, KeyEvent, WindowEvent};
+    use winit::event::{ElementState, Event, KeyEvent, WindowEvent};
     use winit::event_loop::{ActiveEventLoop, EventLoop};
     use winit::raw_window_handle::HasRawWindowHandle;
-    use winit::window::{Window, WindowId};
+    use winit::window::Window;
 
     #[path = "util/fill.rs"]
     mod fill;
 
-    #[derive(Default)]
-    struct Application {
-        parent_window_id: Option<WindowId>,
-        windows: HashMap<WindowId, Window>,
-    }
-
-    impl ApplicationHandler for Application {
-        fn resumed(&mut self, event_loop: &ActiveEventLoop) {
-            let attributes = Window::default_attributes()
-                .with_title("parent window")
-                .with_position(Position::Logical(LogicalPosition::new(0.0, 0.0)))
-                .with_inner_size(LogicalSize::new(640.0f32, 480.0f32));
-            let window = event_loop.create_window(attributes).unwrap();
-
-            println!("Parent window id: {:?})", window.id());
-            self.parent_window_id = Some(window.id());
-
-            self.windows.insert(window.id(), window);
-        }
-
-        fn window_event(
-            &mut self,
-            event_loop: &ActiveEventLoop,
-            window_id: winit::window::WindowId,
-            event: WindowEvent,
-        ) {
-            match event {
-                WindowEvent::CloseRequested => {
-                    self.windows.clear();
-                    event_loop.exit();
-                },
-                WindowEvent::CursorEntered { device_id: _ } => {
-                    // On x11, println when the cursor entered in a window even if the child window
-                    // is created by some key inputs.
-                    // the child windows are always placed at (0, 0) with size (200, 200) in the
-                    // parent window, so we also can see this log when we move
-                    // the cursor around (200, 200) in parent window.
-                    println!("cursor entered in the window {window_id:?}");
-                },
-                WindowEvent::KeyboardInput {
-                    event: KeyEvent { state: ElementState::Pressed, .. },
-                    ..
-                } => {
-                    let parent_window = self.windows.get(&self.parent_window_id.unwrap()).unwrap();
-                    let child_window = spawn_child_window(parent_window, event_loop);
-                    let child_id = child_window.id();
-                    println!("Child window created with id: {child_id:?}");
-                    self.windows.insert(child_id, child_window);
-                },
-                WindowEvent::RedrawRequested => {
-                    if let Some(window) = self.windows.get(&window_id) {
-                        fill::fill_window(window);
-                    }
-                },
-                _ => (),
-            }
-        }
-    }
-
     fn spawn_child_window(parent: &Window, event_loop: &ActiveEventLoop) -> Window {
         let parent = parent.raw_window_handle().unwrap();
         let mut window_attributes = Window::default_attributes()
@@ -85,9 +25,58 @@ fn main() -> Result<(), impl std::error::Error> {
         event_loop.create_window(window_attributes).unwrap()
     }
 
+    let mut windows = HashMap::new();
+
     let event_loop: EventLoop<()> = EventLoop::new().unwrap();
-    let mut app = Application::default();
-    event_loop.run_app(&mut app)
+    let mut parent_window_id = None;
+
+    event_loop.run(move |event: Event<()>, event_loop| {
+        match event {
+            Event::Resumed => {
+                let attributes = Window::default_attributes()
+                    .with_title("parent window")
+                    .with_position(Position::Logical(LogicalPosition::new(0.0, 0.0)))
+                    .with_inner_size(LogicalSize::new(640.0f32, 480.0f32));
+                let window = event_loop.create_window(attributes).unwrap();
+
+                parent_window_id = Some(window.id());
+
+                println!("Parent window id: {parent_window_id:?})");
+                windows.insert(window.id(), window);
+            },
+            Event::WindowEvent { window_id, event } => match event {
+                WindowEvent::CloseRequested => {
+                    windows.clear();
+                    event_loop.exit();
+                },
+                WindowEvent::CursorEntered { device_id: _ } => {
+                    // On x11, println when the cursor entered in a window even if the child window
+                    // is created by some key inputs.
+                    // the child windows are always placed at (0, 0) with size (200, 200) in the
+                    // parent window, so we also can see this log when we move
+                    // the cursor around (200, 200) in parent window.
+                    println!("cursor entered in the window {window_id:?}");
+                },
+                WindowEvent::KeyboardInput {
+                    event: KeyEvent { state: ElementState::Pressed, .. },
+                    ..
+                } => {
+                    let parent_window = windows.get(&parent_window_id.unwrap()).unwrap();
+                    let child_window = spawn_child_window(parent_window, event_loop);
+                    let child_id = child_window.id();
+                    println!("Child window created with id: {child_id:?}");
+                    windows.insert(child_id, child_window);
+                },
+                WindowEvent::RedrawRequested => {
+                    if let Some(window) = windows.get(&window_id) {
+                        fill::fill_window(window);
+                    }
+                },
+                _ => (),
+            },
+            _ => (),
+        }
+    })
 }
 
 #[cfg(all(feature = "rwh_06", not(any(x11_platform, macos_platform, windows_platform))))]

examples/window.rs

@@ -17,9 +17,7 @@ use softbuffer::{Context, Surface};
 
 use winit::application::ApplicationHandler;
 use winit::dpi::{LogicalSize, PhysicalPosition, PhysicalSize};
-use winit::event::{
-    DeviceEvent, DeviceId, Ime, MouseButton, MouseScrollDelta, StartCause, WindowEvent,
-};
+use winit::event::{DeviceEvent, DeviceId, Ime, MouseButton, MouseScrollDelta, WindowEvent};
 use winit::event_loop::{ActiveEventLoop, EventLoop};
 use winit::keyboard::{Key, ModifiersState};
 use winit::window::{
@@ -214,6 +212,12 @@ impl Application {
             Action::PrintHelp => self.print_help(),
             #[cfg(macos_platform)]
             Action::CycleOptionAsAlt => window.cycle_option_as_alt(),
+            Action::SetTheme(theme) => {
+                window.window.set_theme(theme);
+                // Get the resulting current theme to draw with
+                let actual_theme = theme.or_else(|| window.window.theme()).unwrap_or(Theme::Dark);
+                window.set_draw_theme(actual_theme);
+            },
             #[cfg(macos_platform)]
             Action::CreateNewTab => {
                 let tab_id = window.window.tabbing_identifier();
@@ -305,12 +309,6 @@ impl Application {
 }
 
 impl ApplicationHandler<UserEvent> for Application {
-    fn new_events(&mut self, _event_loop: &ActiveEventLoop, start_cause: StartCause) {
-        if let StartCause::Init = start_cause {
-            info!("Started the event loop");
-        }
-    }
-
     fn user_event(&mut self, _event_loop: &ActiveEventLoop, event: UserEvent) {
         info!("User event: {event:?}");
     }
@@ -328,7 +326,6 @@ impl ApplicationHandler<UserEvent> for Application {
 
         match event {
             WindowEvent::Resized(size) => {
-                info!("Resized({size:?})");
                 window.resize(size);
             },
             WindowEvent::Focused(focused) => {
@@ -343,7 +340,7 @@ impl ApplicationHandler<UserEvent> for Application {
             },
             WindowEvent::ThemeChanged(theme) => {
                 info!("Theme changed to {theme:?}");
-                window.set_theme(theme);
+                window.set_draw_theme(theme);
             },
             WindowEvent::RedrawRequested => {
                 if let Err(err) = window.draw() {
@@ -742,8 +739,8 @@ impl WindowState {
         self.window.request_redraw();
     }
 
-    /// Change the theme.
-    fn set_theme(&mut self, theme: Theme) {
+    /// Change the theme that things are drawn in.
+    fn set_draw_theme(&mut self, theme: Theme) {
         self.theme = theme;
         self.window.request_redraw();
     }
@@ -893,6 +890,7 @@ enum Action {
     ShowWindowMenu,
     #[cfg(macos_platform)]
     CycleOptionAsAlt,
+    SetTheme(Option<Theme>),
     #[cfg(macos_platform)]
     CreateNewTab,
     RequestResize,
@@ -924,6 +922,9 @@ impl Action {
             Action::ShowWindowMenu => "Show window menu",
             #[cfg(macos_platform)]
             Action::CycleOptionAsAlt => "Cycle option as alt mode",
+            Action::SetTheme(None) => "Change to the system theme",
+            Action::SetTheme(Some(Theme::Light)) => "Change to a light theme",
+            Action::SetTheme(Some(Theme::Dark)) => "Change to a dark theme",
             #[cfg(macos_platform)]
             Action::CreateNewTab => "Create new tab",
             Action::RequestResize => "Request a resize",
@@ -1068,6 +1069,10 @@ const KEY_BINDINGS: &[Binding<&'static str>] = &[
         Action::AnimationCustomCursor,
     ),
     Binding::new("Z", ModifiersState::CONTROL, Action::ToggleCursorVisibility),
+    // K.
+    Binding::new("K", ModifiersState::empty(), Action::SetTheme(None)),
+    Binding::new("K", ModifiersState::SUPER, Action::SetTheme(Some(Theme::Light))),
+    Binding::new("K", ModifiersState::CONTROL, Action::SetTheme(Some(Theme::Dark))),
     #[cfg(macos_platform)]
     Binding::new("T", ModifiersState::SUPER, Action::CreateNewTab),
     #[cfg(macos_platform)]

src/changelog/unreleased.md

@@ -12,7 +12,6 @@ on how to add them:
 ### Added
 
 - Add `Window::turbo()`, implemented on X11, Wayland, and Web.
-- Add traits `EventLoopExtWayland` and `EventLoopExtX11`, providing methods `is_wayland` and `is_x11` on `EventLoop`.
 - On X11, add `Window::some_rare_api`.
 - On X11, add `Window::even_more_rare_api`.
 - On Wayland, add `Window::common_api`.
@@ -40,19 +39,3 @@ The migration guide could reference other migration examples in the current
 changelog entry.
 
 ## Unreleased
-
-### Added
-
-- Reexport `raw-window-handle` versions 0.4 and 0.5 as `raw_window_handle_04` and `raw_window_handle_05`.
-- Implement `ApplicationHandler` for `&mut` references and heap allocations to something that implements `ApplicationHandler`.
-
-### Removed
-
-- Remove `EventLoop::run`.
-- Remove `EventLoopExtRunOnDemand::run_on_demand`.
-- Remove `EventLoopExtPumpEvents::pump_events`.
-
-### Fixed
-
-- On macOS, fix panic on exit when dropping windows outside the event loop.
-- On macOS, fix window dragging glitches when dragging across a monitor boundary with different scale factor.

src/changelog/v0.30.md

@@ -1,3 +1,49 @@
+## 0.30.3
+
+### Added
+
+- On Web, add `EventLoopExtWebSys::(set_)poll_strategy()` to allow setting
+  control flow strategies before starting the event loop.
+- On Web, add `WaitUntilStrategy`, which allows to set different strategies for
+  `ControlFlow::WaitUntil`. By default the Prioritized Task Scheduling API is
+  used, with a fallback to `setTimeout()` with a trick to circumvent throttling
+  to 4ms. But an option to use a Web worker to schedule the timer is available
+  as well, which commonly prevents any throttling when the window is not focused.
+
+### Changed
+
+- On macOS, set the window theme on the `NSWindow` instead of application-wide.
+
+### Fixed
+
+- On X11, build on arm platforms.
+- On macOS, fixed `WindowBuilder::with_theme` not having any effect on the window.
+
+## 0.30.2
+
+### Fixed
+
+- On Web, fix `EventLoopProxy::send_event()` triggering event loop immediately
+  when not called from inside the event loop. Now queues a microtask instead.
+- On Web, stop overwriting default cursor with `CursorIcon::Default`.
+- On Web, prevent crash when using `InnerSizeWriter::request_inner_size()`.
+- On macOS, fix not working opacity for entire window.
+
+## 0.30.1
+
+### Added
+
+- Reexport `raw-window-handle` versions 0.4 and 0.5 as `raw_window_handle_04` and `raw_window_handle_05`.
+- Implement `ApplicationHandler` for `&mut` references and heap allocations to something that implements `ApplicationHandler`.
+
+### Fixed
+
+- On macOS, fix panic on exit when dropping windows outside the event loop.
+- On macOS, fix window dragging glitches when dragging across a monitor boundary with different scale factor.
+- On macOS, fix the range in `Ime::Preedit`.
+- On macOS, use the system's internal mechanisms for queuing events.
+- On macOS, handle events directly instead of queuing when possible.
+
 ## 0.30.0
 
 ### Added
@@ -65,7 +111,7 @@
   `Fn`. The semantics are mostly the same, given that the capture list of the
   closure is your new `State`. Consider the following code:
 
-  ```rust,no_run,ignore
+  ```rust,no_run
   use winit::event::Event;
   use winit::event_loop::EventLoop;
   use winit::window::Window;

src/event.rs

@@ -389,6 +389,8 @@ pub enum WindowEvent {
     /// Applications might wish to react to this to change the theme of the content of the window
     /// when the system changes the window theme.
     ///
+    /// This only reports a change if the window theme was not overridden by [`Window::set_theme`].
+    ///
     /// ## Platform-specific
     ///
     /// - **iOS / Android / X11 / Wayland / Orbital:** Unsupported.

src/event_loop.rs

@@ -20,6 +20,7 @@ use web_time::{Duration, Instant};
 
 use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, OsError};
+use crate::event::Event;
 use crate::monitor::MonitorHandle;
 use crate::platform_impl;
 use crate::window::{CustomCursor, CustomCursorSource, Window, WindowAttributes};
@@ -151,7 +152,6 @@ impl fmt::Debug for ActiveEventLoop {
 /// Defaults to [`Wait`].
 ///
 /// [`Wait`]: Self::Wait
-/// [`Event::AboutToWait`]: crate::event::Event::AboutToWait
 #[derive(Copy, Clone, Debug, Default, PartialEq, Eq)]
 pub enum ControlFlow {
     /// When the current loop iteration finishes, immediately begin a new iteration regardless of
@@ -209,110 +209,6 @@ impl EventLoop<()> {
     }
 }
 
-#[cfg(debug_assertions)]
-pub(crate) fn ensure_event_order<'a, T: 'static>(
-    handler: impl ApplicationHandler<T> + 'a,
-) -> impl ApplicationHandler<T> + 'a {
-    use crate::event::{DeviceEvent, DeviceId, StartCause, WindowEvent};
-    use crate::window::WindowId;
-
-    #[derive(Default, Debug, PartialEq, Eq, Clone)]
-    enum State {
-        #[default]
-        NotRunning,
-        Suspended,
-        Running,
-        Waiting,
-    }
-
-    impl State {
-        #[track_caller]
-        fn expect(&self, expected: State) {
-            if *self != expected {
-                tracing::error!("expected state to be {expected:?}, found {self:?}");
-            }
-        }
-
-        #[track_caller]
-        fn transition(&mut self, from: State, to: State) {
-            if *self != from {
-                tracing::error!(
-                    "invalid state transition to {to:?}. Expected {from:?}, found {self:?}"
-                );
-            }
-            *self = to;
-        }
-    }
-
-    struct EnsureEventOrder<A> {
-        inner: A,
-        state: State,
-    }
-
-    impl<A: ApplicationHandler<T>, T: 'static> ApplicationHandler<T> for EnsureEventOrder<A> {
-        fn new_events(&mut self, event_loop: &ActiveEventLoop, cause: StartCause) {
-            match cause {
-                StartCause::Init => self.state.transition(State::NotRunning, State::Suspended),
-                _ => self.state.transition(State::Waiting, State::Running),
-            }
-
-            self.inner.new_events(event_loop, cause);
-        }
-
-        fn resumed(&mut self, event_loop: &ActiveEventLoop) {
-            self.state.transition(State::Suspended, State::Running);
-            self.inner.resumed(event_loop);
-        }
-
-        fn suspended(&mut self, event_loop: &ActiveEventLoop) {
-            self.state.transition(State::Running, State::Suspended);
-            self.inner.suspended(event_loop);
-        }
-
-        fn about_to_wait(&mut self, event_loop: &ActiveEventLoop) {
-            self.state.transition(State::Running, State::Waiting);
-            self.inner.about_to_wait(event_loop);
-        }
-
-        fn exiting(&mut self, event_loop: &ActiveEventLoop) {
-            self.state.transition(State::Suspended, State::NotRunning);
-            self.inner.exiting(event_loop);
-        }
-
-        fn user_event(&mut self, event_loop: &ActiveEventLoop, event: T) {
-            self.state.expect(State::Running);
-            self.inner.user_event(event_loop, event);
-        }
-
-        fn window_event(
-            &mut self,
-            event_loop: &ActiveEventLoop,
-            window_id: WindowId,
-            event: WindowEvent,
-        ) {
-            self.state.expect(State::Running);
-            self.inner.window_event(event_loop, window_id, event);
-        }
-
-        fn device_event(
-            &mut self,
-            event_loop: &ActiveEventLoop,
-            device_id: DeviceId,
-            event: DeviceEvent,
-        ) {
-            self.state.expect(State::Running);
-            self.inner.device_event(event_loop, device_id, event);
-        }
-
-        fn memory_warning(&mut self, event_loop: &ActiveEventLoop) {
-            // TODO: What states are allowed when receiving this?
-            self.inner.memory_warning(event_loop);
-        }
-    }
-
-    EnsureEventOrder { inner: handler, state: State::NotRunning }
-}
-
 impl<T> EventLoop<T> {
     /// Start building a new event loop, with the given type as the user event
     /// type.
@@ -320,6 +216,21 @@ impl<T> EventLoop<T> {
         EventLoopBuilder { platform_specific: Default::default(), _p: PhantomData }
     }
 
+    /// See [`run_app`].
+    ///
+    /// [`run_app`]: Self::run_app
+    #[inline]
+    #[deprecated = "use `EventLoop::run_app` instead"]
+    #[cfg(not(all(web_platform, target_feature = "exception-handling")))]
+    pub fn run<F>(self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &ActiveEventLoop),
+    {
+        let _span = tracing::debug_span!("winit::EventLoop::run").entered();
+
+        self.event_loop.run(event_handler)
+    }
+
     /// Run the application with the event loop on the calling thread.
     ///
     /// See the [`set_control_flow()`] docs on how to change the event loop's behavior.
@@ -351,9 +262,7 @@ impl<T> EventLoop<T> {
     #[inline]
     #[cfg(not(all(web_platform, target_feature = "exception-handling")))]
     pub fn run_app<A: ApplicationHandler<T>>(self, app: &mut A) -> Result<(), EventLoopError> {
-        #[cfg(debug_assertions)]
-        let app = &mut ensure_event_order(app);
-        self.event_loop.run_app(app)
+        self.event_loop.run(|event, event_loop| dispatch_event_for_app(app, event_loop, event))
     }
 
     /// Creates an [`EventLoopProxy`] that can be used to dispatch user events
@@ -540,7 +449,7 @@ impl ActiveEventLoop {
 
     /// This exits the event loop.
     ///
-    /// See [`LoopExiting`][crate::event::Event::LoopExiting].
+    /// See [`LoopExiting`][Event::LoopExiting].
     pub fn exit(&self) {
         let _span = tracing::debug_span!("winit::ActiveEventLoop::exit",).entered();
 
@@ -709,3 +618,23 @@ impl AsyncRequestSerial {
         Self { serial }
     }
 }
+
+/// Shim for various run APIs.
+#[inline(always)]
+pub(crate) fn dispatch_event_for_app<T: 'static, A: ApplicationHandler<T>>(
+    app: &mut A,
+    event_loop: &ActiveEventLoop,
+    event: Event<T>,
+) {
+    match event {
+        Event::NewEvents(cause) => app.new_events(event_loop, cause),
+        Event::WindowEvent { window_id, event } => app.window_event(event_loop, window_id, event),
+        Event::DeviceEvent { device_id, event } => app.device_event(event_loop, device_id, event),
+        Event::UserEvent(event) => app.user_event(event_loop, event),
+        Event::Suspended => app.suspended(event_loop),
+        Event::Resumed => app.resumed(event_loop),
+        Event::AboutToWait => app.about_to_wait(event_loop),
+        Event::LoopExiting => app.exiting(event_loop),
+        Event::MemoryWarning => app.memory_warning(event_loop),
+    }
+}

src/platform/android.rs

@@ -62,7 +62,7 @@
 //! If your application is currently based on `NativeActivity` via the `ndk-glue` crate and building
 //! with `cargo apk`, then the minimal changes would be:
 //! 1. Remove `ndk-glue` from your `Cargo.toml`
-//! 2. Enable the `"android-native-activity"` feature for Winit: `winit = { version = "0.30.0",
+//! 2. Enable the `"android-native-activity"` feature for Winit: `winit = { version = "0.30.3",
 //!    features = [ "android-native-activity" ] }`
 //! 3. Add an `android_main` entrypoint (as above), instead of using the '`[ndk_glue::main]` proc
 //!    macro from `ndk-macros` (optionally add a dependency on `android_logger` and initialize

src/platform/pump_events.rs

@@ -1,13 +1,12 @@
 use std::time::Duration;
 
 use crate::application::ApplicationHandler;
-use crate::event_loop::EventLoop;
+use crate::event::Event;
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 
 /// Additional methods on [`EventLoop`] for pumping events within an external event loop
 pub trait EventLoopExtPumpEvents {
     /// A type provided by the user that can be passed through [`Event::UserEvent`].
-    ///
-    /// [`Event::UserEvent`]: crate::event::Event::UserEvent
     type UserEvent: 'static;
 
     /// Pump the `EventLoop` to check for and dispatch pending events.
@@ -108,18 +107,30 @@ pub trait EventLoopExtPumpEvents {
         &mut self,
         timeout: Option<Duration>,
         app: &mut A,
-    ) -> PumpStatus;
+    ) -> PumpStatus {
+        #[allow(deprecated)]
+        self.pump_events(timeout, |event, event_loop| {
+            event_loop::dispatch_event_for_app(app, event_loop, event)
+        })
+    }
+
+    /// See [`pump_app_events`].
+    ///
+    /// [`pump_app_events`]: Self::pump_app_events
+    #[deprecated = "use EventLoopExtPumpEvents::pump_app_events"]
+    fn pump_events<F>(&mut self, timeout: Option<Duration>, event_handler: F) -> PumpStatus
+    where
+        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
 }
 
 impl<T> EventLoopExtPumpEvents for EventLoop<T> {
     type UserEvent = T;
 
-    fn pump_app_events<A: ApplicationHandler<Self::UserEvent>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
-        self.event_loop.pump_app_events(timeout, app)
+    fn pump_events<F>(&mut self, timeout: Option<Duration>, event_handler: F) -> PumpStatus
+    where
+        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop),
+    {
+        self.event_loop.pump_events(timeout, event_handler)
     }
 }
 

src/platform/run_on_demand.rs

@@ -1,6 +1,7 @@
 use crate::application::ApplicationHandler;
 use crate::error::EventLoopError;
-use crate::event_loop::{ActiveEventLoop, EventLoop};
+use crate::event::Event;
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 
 #[cfg(doc)]
 use crate::{platform::pump_events::EventLoopExtPumpEvents, window::Window};
@@ -8,10 +9,16 @@ use crate::{platform::pump_events::EventLoopExtPumpEvents, window::Window};
 /// Additional methods on [`EventLoop`] to return control flow to the caller.
 pub trait EventLoopExtRunOnDemand {
     /// A type provided by the user that can be passed through [`Event::UserEvent`].
-    ///
-    /// [`Event::UserEvent`]: crate::event::Event::UserEvent
     type UserEvent: 'static;
 
+    /// See [`run_app_on_demand`].
+    ///
+    /// [`run_app_on_demand`]: Self::run_app_on_demand
+    #[deprecated = "use EventLoopExtRunOnDemand::run_app_on_demand"]
+    fn run_on_demand<F>(&mut self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
+
     /// Run the application with the event loop on the calling thread.
     ///
     /// Unlike [`EventLoop::run_app`], this function accepts non-`'static` (i.e. non-`move`)
@@ -61,18 +68,23 @@ pub trait EventLoopExtRunOnDemand {
     fn run_app_on_demand<A: ApplicationHandler<Self::UserEvent>>(
         &mut self,
         app: &mut A,
-    ) -> Result<(), EventLoopError>;
+    ) -> Result<(), EventLoopError> {
+        #[allow(deprecated)]
+        self.run_on_demand(|event, event_loop| {
+            event_loop::dispatch_event_for_app(app, event_loop, event)
+        })
+    }
 }
 
 impl<T> EventLoopExtRunOnDemand for EventLoop<T> {
     type UserEvent = T;
 
-    fn run_app_on_demand<A: ApplicationHandler<Self::UserEvent>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
+    fn run_on_demand<F>(&mut self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<Self::UserEvent>, &ActiveEventLoop),
+    {
         self.event_loop.window_target().clear_exit();
-        self.event_loop.run_app_on_demand(app)
+        self.event_loop.run_on_demand(event_handler)
     }
 }
 

src/platform/web.rs

@@ -55,7 +55,8 @@ use web_sys::HtmlCanvasElement;
 
 use crate::application::ApplicationHandler;
 use crate::cursor::CustomCursorSource;
-use crate::event_loop::{ActiveEventLoop, EventLoop};
+use crate::event::Event;
+use crate::event_loop::{self, ActiveEventLoop, EventLoop};
 #[cfg(web_platform)]
 use crate::platform_impl::CustomCursorFuture as PlatformCustomCursorFuture;
 use crate::platform_impl::PlatformCustomCursorSource;
@@ -155,9 +156,7 @@ impl WindowAttributesExtWebSys for WindowAttributes {
 
 /// Additional methods on `EventLoop` that are specific to the web.
 pub trait EventLoopExtWebSys {
-    /// A type provided by the user that can be passed through [`Event::UserEvent`].
-    ///
-    /// [`Event::UserEvent`]: crate::event::Event::UserEvent
+    /// A type provided by the user that can be passed through `Event::UserEvent`.
     type UserEvent: 'static;
 
     /// Initializes the winit event loop.
@@ -183,13 +182,74 @@ pub trait EventLoopExtWebSys {
     )]
     /// [^1]: `run_app()` is _not_ available on WASM when the target supports `exception-handling`.
     fn spawn_app<A: ApplicationHandler<Self::UserEvent> + 'static>(self, app: A);
+
+    /// See [`spawn_app`].
+    ///
+    /// [`spawn_app`]: Self::spawn_app
+    #[deprecated = "use EventLoopExtWebSys::spawn_app"]
+    fn spawn<F>(self, event_handler: F)
+    where
+        F: 'static + FnMut(Event<Self::UserEvent>, &ActiveEventLoop);
+
+    /// Sets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn set_poll_strategy(&self, strategy: PollStrategy);
+
+    /// Gets the strategy for [`ControlFlow::Poll`].
+    ///
+    /// See [`PollStrategy`].
+    ///
+    /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
+    fn poll_strategy(&self) -> PollStrategy;
+
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
 }
 
 impl<T> EventLoopExtWebSys for EventLoop<T> {
     type UserEvent = T;
 
-    fn spawn_app<A: ApplicationHandler<Self::UserEvent> + 'static>(self, app: A) {
-        self.event_loop.spawn_app(app);
+    fn spawn_app<A: ApplicationHandler<Self::UserEvent> + 'static>(self, mut app: A) {
+        self.event_loop.spawn(move |event, event_loop| {
+            event_loop::dispatch_event_for_app(&mut app, event_loop, event)
+        });
+    }
+
+    fn spawn<F>(self, event_handler: F)
+    where
+        F: 'static + FnMut(Event<Self::UserEvent>, &ActiveEventLoop),
+    {
+        self.event_loop.spawn(event_handler)
+    }
+
+    fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.event_loop.set_poll_strategy(strategy);
+    }
+
+    fn poll_strategy(&self) -> PollStrategy {
+        self.event_loop.poll_strategy()
+    }
+
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.event_loop.set_wait_until_strategy(strategy);
+    }
+
+    fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.event_loop.wait_until_strategy()
     }
 }
 
@@ -208,6 +268,20 @@ pub trait ActiveEventLoopExtWebSys {
     /// [`ControlFlow::Poll`]: crate::event_loop::ControlFlow::Poll
     fn poll_strategy(&self) -> PollStrategy;
 
+    /// Sets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy);
+
+    /// Gets the strategy for [`ControlFlow::WaitUntil`].
+    ///
+    /// See [`WaitUntilStrategy`].
+    ///
+    /// [`ControlFlow::WaitUntil`]: crate::event_loop::ControlFlow::WaitUntil
+    fn wait_until_strategy(&self) -> WaitUntilStrategy;
+
     /// Async version of [`ActiveEventLoop::create_custom_cursor()`] which waits until the
     /// cursor has completely finished loading.
     fn create_custom_cursor_async(&self, source: CustomCursorSource) -> CustomCursorFuture;
@@ -228,6 +302,16 @@ impl ActiveEventLoopExtWebSys for ActiveEventLoop {
     fn poll_strategy(&self) -> PollStrategy {
         self.p.poll_strategy()
     }
+
+    #[inline]
+    fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.p.set_wait_until_strategy(strategy);
+    }
+
+    #[inline]
+    fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.p.wait_until_strategy()
+    }
 }
 
 /// Strategy used for [`ControlFlow::Poll`][crate::event_loop::ControlFlow::Poll].
@@ -256,6 +340,29 @@ pub enum PollStrategy {
     Scheduler,
 }
 
+/// Strategy used for [`ControlFlow::WaitUntil`][crate::event_loop::ControlFlow::WaitUntil].
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
+pub enum WaitUntilStrategy {
+    /// Uses the [Prioritized Task Scheduling API] to queue the next event loop. If not available
+    /// this will fallback to [`setTimeout()`].
+    ///
+    /// This strategy is commonly not affected by browser throttling unless the window is not
+    /// focused.
+    ///
+    /// This is the default strategy.
+    ///
+    /// [Prioritized Task Scheduling API]: https://developer.mozilla.org/en-US/docs/Web/API/Prioritized_Task_Scheduling_API
+    /// [`setTimeout()`]: https://developer.mozilla.org/en-US/docs/Web/API/setTimeout
+    #[default]
+    Scheduler,
+    /// Equal to [`Scheduler`][Self::Scheduler] but wakes up the event loop from a [worker].
+    ///
+    /// This strategy is commonly not affected by browser throttling regardless of window focus.
+    ///
+    /// [worker]: https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API
+    Worker,
+}
+
 pub trait CustomCursorExtWebSys {
     /// Returns if this cursor is an animation.
     fn is_animation(&self) -> bool;

src/platform_impl/android/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(android_platform)]
-
 use std::cell::Cell;
 use std::collections::VecDeque;
 use std::hash::Hash;
@@ -14,13 +12,12 @@ use android_activity::{
 };
 use tracing::{debug, trace, warn};
 
-use crate::application::ApplicationHandler;
 use crate::cursor::Cursor;
 use crate::dpi::{PhysicalPosition, PhysicalSize, Position, Size};
 use crate::error;
 use crate::error::EventLoopError;
 use crate::event::{self, Force, InnerSizeWriter, StartCause};
-use crate::event_loop::{self, ControlFlow, DeviceEvents};
+use crate::event_loop::{self, ActiveEventLoop as RootAEL, ControlFlow, DeviceEvents};
 use crate::platform::pump_events::PumpStatus;
 use crate::platform_impl::Fullscreen;
 use crate::window::{
@@ -198,28 +195,27 @@ impl<T: 'static> EventLoop<T> {
         })
     }
 
-    fn single_iteration<A: ApplicationHandler<T>>(
-        &mut self,
-        main_event: Option<MainEvent<'_>>,
-        app: &mut A,
-    ) {
+    fn single_iteration<F>(&mut self, main_event: Option<MainEvent<'_>>, callback: &mut F)
+    where
+        F: FnMut(event::Event<T>, &RootAEL),
+    {
         trace!("Mainloop iteration");
 
         let cause = self.cause;
         let mut pending_redraw = self.pending_redraw;
         let mut resized = false;
 
-        app.new_events(self.window_target(), cause);
+        callback(event::Event::NewEvents(cause), self.window_target());
 
         if let Some(event) = main_event {
             trace!("Handling main event {:?}", event);
 
             match event {
                 MainEvent::InitWindow { .. } => {
-                    app.resumed(self.window_target());
+                    callback(event::Event::Resumed, self.window_target());
                 },
                 MainEvent::TerminateWindow { .. } => {
-                    app.suspended(self.window_target());
+                    callback(event::Event::Suspended, self.window_target());
                 },
                 MainEvent::WindowResized { .. } => resized = true,
                 MainEvent::RedrawNeeded { .. } => pending_redraw = true,
@@ -228,15 +224,23 @@ impl<T: 'static> EventLoop<T> {
                 },
                 MainEvent::GainedFocus => {
                     HAS_FOCUS.store(true, Ordering::Relaxed);
-                    let window_id = window::WindowId(WindowId);
-                    let event = event::WindowEvent::Focused(true);
-                    app.window_event(self.window_target(), window_id, event);
+                    callback(
+                        event::Event::WindowEvent {
+                            window_id: window::WindowId(WindowId),
+                            event: event::WindowEvent::Focused(true),
+                        },
+                        self.window_target(),
+                    );
                 },
                 MainEvent::LostFocus => {
                     HAS_FOCUS.store(false, Ordering::Relaxed);
-                    let window_id = window::WindowId(WindowId);
-                    let event = event::WindowEvent::Focused(false);
-                    app.window_event(self.window_target(), window_id, event);
+                    callback(
+                        event::Event::WindowEvent {
+                            window_id: window::WindowId(WindowId),
+                            event: event::WindowEvent::Focused(false),
+                        },
+                        self.window_target(),
+                    );
                 },
                 MainEvent::ConfigChanged { .. } => {
                     let monitor = MonitorHandle::new(self.android_app.clone());
@@ -246,19 +250,20 @@ impl<T: 'static> EventLoop<T> {
                         let new_inner_size = Arc::new(Mutex::new(
                             MonitorHandle::new(self.android_app.clone()).size(),
                         ));
-                        let window_id = window::WindowId(WindowId);
-                        let event = event::WindowEvent::ScaleFactorChanged {
-                            inner_size_writer: InnerSizeWriter::new(Arc::downgrade(
-                                &new_inner_size,
-                            )),
-                            scale_factor,
+                        let event = event::Event::WindowEvent {
+                            window_id: window::WindowId(WindowId),
+                            event: event::WindowEvent::ScaleFactorChanged {
+                                inner_size_writer: InnerSizeWriter::new(Arc::downgrade(
+                                    &new_inner_size,
+                                )),
+                                scale_factor,
+                            },
                         };
-
-                        app.window_event(self.window_target(), window_id, event);
+                        callback(event, self.window_target());
                     }
                 },
                 MainEvent::LowMemory => {
-                    app.memory_warning(self.window_target());
+                    callback(event::Event::MemoryWarning, self.window_target());
                 },
                 MainEvent::Start => {
                     // XXX: how to forward this state to applications?
@@ -306,7 +311,7 @@ impl<T: 'static> EventLoop<T> {
         match android_app.input_events_iter() {
             Ok(mut input_iter) => loop {
                 let read_event =
-                    input_iter.next(|event| self.handle_input_event(&android_app, event, app));
+                    input_iter.next(|event| self.handle_input_event(&android_app, event, callback));
 
                 if !read_event {
                     break;
@@ -320,7 +325,7 @@ impl<T: 'static> EventLoop<T> {
         // Empty the user event buffer
         {
             while let Ok(event) = self.user_events_receiver.try_recv() {
-                app.user_event(self.window_target(), event);
+                callback(crate::event::Event::UserEvent(event), self.window_target());
             }
         }
 
@@ -333,32 +338,39 @@ impl<T: 'static> EventLoop<T> {
                 } else {
                     PhysicalSize::new(0, 0)
                 };
-                let window_id = window::WindowId(WindowId);
-                let event = event::WindowEvent::Resized(size);
-                app.window_event(self.window_target(), window_id, event);
+                let event = event::Event::WindowEvent {
+                    window_id: window::WindowId(WindowId),
+                    event: event::WindowEvent::Resized(size),
+                };
+                callback(event, self.window_target());
             }
 
             pending_redraw |= self.redraw_flag.get_and_reset();
             if pending_redraw {
                 pending_redraw = false;
-                let window_id = window::WindowId(WindowId);
-                let event = event::WindowEvent::RedrawRequested;
-                app.window_event(self.window_target(), window_id, event);
+                let event = event::Event::WindowEvent {
+                    window_id: window::WindowId(WindowId),
+                    event: event::WindowEvent::RedrawRequested,
+                };
+                callback(event, self.window_target());
             }
         }
 
         // This is always the last event we dispatch before poll again
-        app.about_to_wait(self.window_target());
+        callback(event::Event::AboutToWait, self.window_target());
 
         self.pending_redraw = pending_redraw;
     }
 
-    fn handle_input_event<A: ApplicationHandler<T>>(
+    fn handle_input_event<F>(
         &mut self,
         android_app: &AndroidApp,
         event: &InputEvent<'_>,
-        app: &mut A,
-    ) -> InputStatus {
+        callback: &mut F,
+    ) -> InputStatus
+    where
+        F: FnMut(event::Event<T>, &RootAEL),
+    {
         let mut input_status = InputStatus::Handled;
         match event {
             InputEvent::MotionEvent(motion_event) => {
@@ -396,16 +408,17 @@ impl<T: 'static> EventLoop<T> {
                             "Input event {device_id:?}, {phase:?}, loc={location:?}, \
                              pointer={pointer:?}"
                         );
-
-                        let event = event::WindowEvent::Touch(event::Touch {
-                            device_id,
-                            phase,
-                            location,
-                            id: pointer.pointer_id() as u64,
-                            force: Some(Force::Normalized(pointer.pressure() as f64)),
-                        });
-
-                        app.window_event(self.window_target(), window_id, event);
+                        let event = event::Event::WindowEvent {
+                            window_id,
+                            event: event::WindowEvent::Touch(event::Touch {
+                                device_id,
+                                phase,
+                                location,
+                                id: pointer.pointer_id() as u64,
+                                force: Some(Force::Normalized(pointer.pressure() as f64)),
+                            }),
+                        };
+                        callback(event, self.window_target());
                     }
                 }
             },
@@ -433,22 +446,23 @@ impl<T: 'static> EventLoop<T> {
                             &mut self.combining_accent,
                         );
 
-                        let window_id = window::WindowId(WindowId);
-                        let event = event::WindowEvent::KeyboardInput {
-                            device_id: event::DeviceId(DeviceId(key.device_id())),
-                            event: event::KeyEvent {
-                                state,
-                                physical_key: keycodes::to_physical_key(keycode),
-                                logical_key: keycodes::to_logical(key_char, keycode),
-                                location: keycodes::to_location(keycode),
-                                repeat: key.repeat_count() > 0,
-                                text: None,
-                                platform_specific: KeyEventExtra {},
+                        let event = event::Event::WindowEvent {
+                            window_id: window::WindowId(WindowId),
+                            event: event::WindowEvent::KeyboardInput {
+                                device_id: event::DeviceId(DeviceId(key.device_id())),
+                                event: event::KeyEvent {
+                                    state,
+                                    physical_key: keycodes::to_physical_key(keycode),
+                                    logical_key: keycodes::to_logical(key_char, keycode),
+                                    location: keycodes::to_location(keycode),
+                                    repeat: key.repeat_count() > 0,
+                                    text: None,
+                                    platform_specific: KeyEventExtra {},
+                                },
+                                is_synthetic: false,
                             },
-                            is_synthetic: false,
                         };
-
-                        app.window_event(self.window_target(), window_id, event);
+                        callback(event, self.window_target());
                     },
                 }
             },
@@ -460,16 +474,19 @@ impl<T: 'static> EventLoop<T> {
         input_status
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
-        self.run_app_on_demand(app)
+    pub fn run<F>(mut self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(event::Event<T>, &event_loop::ActiveEventLoop),
+    {
+        self.run_on_demand(event_handler)
     }
 
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
+    pub fn run_on_demand<F>(&mut self, mut event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(event::Event<T>, &event_loop::ActiveEventLoop),
+    {
         loop {
-            match self.pump_app_events(None, app) {
+            match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {
                     break Ok(());
                 },
@@ -483,11 +500,10 @@ impl<T: 'static> EventLoop<T> {
         }
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, mut callback: F) -> PumpStatus
+    where
+        F: FnMut(event::Event<T>, &RootAEL),
+    {
         if !self.loop_running {
             self.loop_running = true;
 
@@ -498,18 +514,18 @@ impl<T: 'static> EventLoop<T> {
             self.cause = StartCause::Init;
 
             // run the initial loop iteration
-            self.single_iteration(None, app);
+            self.single_iteration(None, &mut callback);
         }
 
         // Consider the possibility that the `StartCause::Init` iteration could
         // request to Exit
         if !self.exiting() {
-            self.poll_events_with_timeout(timeout, app);
+            self.poll_events_with_timeout(timeout, &mut callback);
         }
         if self.exiting() {
             self.loop_running = false;
 
-            app.exiting(self.window_target());
+            callback(event::Event::LoopExiting, self.window_target());
 
             PumpStatus::Exit(0)
         } else {
@@ -517,11 +533,10 @@ impl<T: 'static> EventLoop<T> {
         }
     }
 
-    fn poll_events_with_timeout<A: ApplicationHandler<T>>(
-        &mut self,
-        mut timeout: Option<Duration>,
-        app: &mut A,
-    ) {
+    fn poll_events_with_timeout<F>(&mut self, mut timeout: Option<Duration>, mut callback: F)
+    where
+        F: FnMut(event::Event<T>, &RootAEL),
+    {
         let start = Instant::now();
 
         self.pending_redraw |= self.redraw_flag.get_and_reset();
@@ -542,8 +557,8 @@ impl<T: 'static> EventLoop<T> {
                 min_timeout(control_flow_timeout, timeout)
             };
 
-        let android_app = self.android_app.clone(); // Don't borrow self as part of poll expression
-        android_app.poll_events(timeout, |poll_event| {
+        let app = self.android_app.clone(); // Don't borrow self as part of poll expression
+        app.poll_events(timeout, |poll_event| {
             let mut main_event = None;
 
             match poll_event {
@@ -584,7 +599,7 @@ impl<T: 'static> EventLoop<T> {
                 },
             };
 
-            self.single_iteration(main_event, app);
+            self.single_iteration(main_event, &mut callback);
         });
     }
 

src/platform_impl/ios/app_delegate.rs

@@ -1,11 +1,9 @@
 use objc2::{declare_class, mutability, ClassType, DeclaredClass};
-use objc2_foundation::{MainThreadMarker, NSObject, NSObjectProtocol};
-use objc2_ui_kit::{UIApplication, UIWindow};
+use objc2_foundation::{MainThreadMarker, NSObject};
+use objc2_ui_kit::UIApplication;
 
-use super::app_state::{self, EventWrapper};
-use super::window::WinitUIWindow;
-use crate::event::{Event, WindowEvent};
-use crate::window::WindowId as RootWindowId;
+use super::app_state::{self, send_occluded_event_for_all_windows, EventWrapper};
+use crate::event::Event;
 
 declare_class!(
     pub struct AppDelegate;
@@ -40,35 +38,17 @@ declare_class!(
 
         #[method(applicationWillEnterForeground:)]
         fn will_enter_foreground(&self, application: &UIApplication) {
-            self.send_occluded_event_for_all_windows(application, false);
+            send_occluded_event_for_all_windows(application, false);
         }
 
         #[method(applicationDidEnterBackground:)]
         fn did_enter_background(&self, application: &UIApplication) {
-            self.send_occluded_event_for_all_windows(application, true);
+            send_occluded_event_for_all_windows(application, true);
         }
 
         #[method(applicationWillTerminate:)]
         fn will_terminate(&self, application: &UIApplication) {
-            let mut events = Vec::new();
-            #[allow(deprecated)]
-            for window in application.windows().iter() {
-                if window.is_kind_of::<WinitUIWindow>() {
-                    // SAFETY: We just checked that the window is a `winit` window
-                    let window = unsafe {
-                        let ptr: *const UIWindow = window;
-                        let ptr: *const WinitUIWindow = ptr.cast();
-                        &*ptr
-                    };
-                    events.push(EventWrapper::StaticEvent(Event::WindowEvent {
-                        window_id: RootWindowId(window.id()),
-                        event: WindowEvent::Destroyed,
-                    }));
-                }
-            }
-            let mtm = MainThreadMarker::new().unwrap();
-            app_state::handle_nonuser_events(mtm, events);
-            app_state::terminated(mtm);
+            app_state::terminated(application);
         }
 
         #[method(applicationDidReceiveMemoryWarning:)]
@@ -78,26 +58,3 @@ declare_class!(
         }
     }
 );
-
-impl AppDelegate {
-    fn send_occluded_event_for_all_windows(&self, application: &UIApplication, occluded: bool) {
-        let mut events = Vec::new();
-        #[allow(deprecated)]
-        for window in application.windows().iter() {
-            if window.is_kind_of::<WinitUIWindow>() {
-                // SAFETY: We just checked that the window is a `winit` window
-                let window = unsafe {
-                    let ptr: *const UIWindow = window;
-                    let ptr: *const WinitUIWindow = ptr.cast();
-                    &*ptr
-                };
-                events.push(EventWrapper::StaticEvent(Event::WindowEvent {
-                    window_id: RootWindowId(window.id()),
-                    event: WindowEvent::Occluded(occluded),
-                }));
-            }
-        }
-        let mtm = MainThreadMarker::new().unwrap();
-        app_state::handle_nonuser_events(mtm, events);
-    }
-}

src/platform_impl/ios/app_state.rs

@@ -20,7 +20,7 @@ use objc2_foundation::{
     CGRect, CGSize, MainThreadMarker, NSInteger, NSObjectProtocol, NSOperatingSystemVersion,
     NSProcessInfo,
 };
-use objc2_ui_kit::{UICoordinateSpace, UIView};
+use objc2_ui_kit::{UIApplication, UICoordinateSpace, UIView, UIWindow};
 
 use super::window::WinitUIWindow;
 use crate::dpi::PhysicalSize;
@@ -662,6 +662,28 @@ fn handle_user_events(mtm: MainThreadMarker) {
     }
 }
 
+pub(crate) fn send_occluded_event_for_all_windows(application: &UIApplication, occluded: bool) {
+    let mtm = MainThreadMarker::from(application);
+
+    let mut events = Vec::new();
+    #[allow(deprecated)]
+    for window in application.windows().iter() {
+        if window.is_kind_of::<WinitUIWindow>() {
+            // SAFETY: We just checked that the window is a `winit` window
+            let window = unsafe {
+                let ptr: *const UIWindow = window;
+                let ptr: *const WinitUIWindow = ptr.cast();
+                &*ptr
+            };
+            events.push(EventWrapper::StaticEvent(Event::WindowEvent {
+                window_id: RootWindowId(window.id()),
+                event: WindowEvent::Occluded(occluded),
+            }));
+        }
+    }
+    handle_nonuser_events(mtm, events);
+}
+
 pub fn handle_main_events_cleared(mtm: MainThreadMarker) {
     let mut this = AppState::get_mut(mtm);
     if !this.has_launched() || this.has_terminated() {
@@ -696,7 +718,27 @@ pub fn handle_events_cleared(mtm: MainThreadMarker) {
     AppState::get_mut(mtm).events_cleared_transition();
 }
 
-pub fn terminated(mtm: MainThreadMarker) {
+pub(crate) fn terminated(application: &UIApplication) {
+    let mtm = MainThreadMarker::from(application);
+
+    let mut events = Vec::new();
+    #[allow(deprecated)]
+    for window in application.windows().iter() {
+        if window.is_kind_of::<WinitUIWindow>() {
+            // SAFETY: We just checked that the window is a `winit` window
+            let window = unsafe {
+                let ptr: *const UIWindow = window;
+                let ptr: *const WinitUIWindow = ptr.cast();
+                &*ptr
+            };
+            events.push(EventWrapper::StaticEvent(Event::WindowEvent {
+                window_id: RootWindowId(window.id()),
+                event: WindowEvent::Destroyed,
+            }));
+        }
+    }
+    handle_nonuser_events(mtm, events);
+
     let mut this = AppState::get_mut(mtm);
     let mut handler = this.terminated_transition();
     drop(this);
@@ -756,7 +798,7 @@ impl EventLoopWaker {
             // future, but that gets changed to fire immediately in did_finish_launching
             let timer = CFRunLoopTimerCreate(
                 ptr::null_mut(),
-                std::f64::MAX,
+                f64::MAX,
                 0.000_000_1,
                 0,
                 0,
@@ -770,11 +812,11 @@ impl EventLoopWaker {
     }
 
     fn stop(&mut self) {
-        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MAX) }
+        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
     }
 
     fn start(&mut self) {
-        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MIN) }
+        unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
     }
 
     fn start_at(&mut self, instant: Instant) {

src/platform_impl/ios/event_loop.rs

@@ -16,7 +16,6 @@ use objc2::{msg_send_id, ClassType};
 use objc2_foundation::{MainThreadMarker, NSString};
 use objc2_ui_kit::{UIApplication, UIApplicationMain, UIDevice, UIScreen, UIUserInterfaceIdiom};
 
-use crate::application::ApplicationHandler;
 use crate::error::EventLoopError;
 use crate::event::Event;
 use crate::event_loop::{
@@ -109,28 +108,17 @@ impl OwnedDisplayHandle {
     }
 }
 
-fn map_user_event<T: 'static, A: ApplicationHandler<T>>(
-    app: &mut A,
+fn map_user_event<T: 'static>(
+    mut handler: impl FnMut(Event<T>, &RootActiveEventLoop),
     receiver: mpsc::Receiver<T>,
-) -> impl FnMut(Event<HandlePendingUserEvents>, &RootActiveEventLoop) + '_ {
-    move |event, window_target| match event {
-        Event::NewEvents(cause) => app.new_events(window_target, cause),
-        Event::WindowEvent { window_id, event } => {
-            app.window_event(window_target, window_id, event)
-        },
-        Event::DeviceEvent { device_id, event } => {
-            app.device_event(window_target, device_id, event)
-        },
-        Event::UserEvent(_) => {
+) -> impl FnMut(Event<HandlePendingUserEvents>, &RootActiveEventLoop) {
+    move |event, window_target| match event.map_nonuser_event() {
+        Ok(event) => (handler)(event, window_target),
+        Err(_) => {
             for event in receiver.try_iter() {
-                app.user_event(window_target, event);
+                (handler)(Event::UserEvent(event), window_target);
             }
         },
-        Event::Suspended => app.suspended(window_target),
-        Event::Resumed => app.resumed(window_target),
-        Event::AboutToWait => app.about_to_wait(window_target),
-        Event::LoopExiting => app.exiting(window_target),
-        Event::MemoryWarning => app.memory_warning(window_target),
     }
 }
 
@@ -173,7 +161,10 @@ impl<T: 'static> EventLoop<T> {
         })
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(self, app: &mut A) -> ! {
+    pub fn run<F>(self, handler: F) -> !
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         let application: Option<Retained<UIApplication>> =
             unsafe { msg_send_id![UIApplication::class(), sharedApplication] };
         assert!(
@@ -183,7 +174,7 @@ impl<T: 'static> EventLoop<T> {
              `EventLoop::run_app` calls `UIApplicationMain` on iOS",
         );
 
-        let handler = map_user_event(app, self.receiver);
+        let handler = map_user_event(handler, self.receiver);
 
         let handler = unsafe {
             std::mem::transmute::<
@@ -283,8 +274,7 @@ impl<T> EventLoopProxy<T> {
                 cancel: None,
                 perform: event_loop_proxy_handler,
             };
-            let source =
-                CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::max_value() - 1, &mut context);
+            let source = CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::MAX - 1, &mut context);
             CFRunLoopAddSource(rl, source, kCFRunLoopCommonModes);
             CFRunLoopWakeUp(rl);
 
@@ -367,7 +357,7 @@ fn setup_control_flow_observers() {
             ptr::null_mut(),
             kCFRunLoopAfterWaiting,
             1, // repeat = true
-            CFIndex::min_value(),
+            CFIndex::MIN,
             control_flow_begin_handler,
             ptr::null_mut(),
         );
@@ -387,7 +377,7 @@ fn setup_control_flow_observers() {
             ptr::null_mut(),
             kCFRunLoopExit | kCFRunLoopBeforeWaiting,
             1, // repeat = true
-            CFIndex::max_value(),
+            CFIndex::MAX,
             control_flow_end_handler,
             ptr::null_mut(),
         );

src/platform_impl/ios/mod.rs

@@ -1,4 +1,3 @@
-#![cfg(ios_platform)]
 #![allow(clippy::let_unit_value)]
 
 mod app_delegate;

src/platform_impl/linux/mod.rs

@@ -11,8 +11,6 @@ use std::{env, fmt};
 #[cfg(x11_platform)]
 use std::{ffi::CStr, mem::MaybeUninit, os::raw::*, sync::Mutex};
 
-use crate::application::ApplicationHandler;
-use crate::platform::pump_events::PumpStatus;
 #[cfg(x11_platform)]
 use crate::utils::Lazy;
 use smol_str::SmolStr;
@@ -21,9 +19,12 @@ use smol_str::SmolStr;
 use self::x11::{X11Error, XConnection, XError, XNotSupported};
 use crate::dpi::{PhysicalPosition, PhysicalSize, Position, Size};
 use crate::error::{EventLoopError, ExternalError, NotSupportedError, OsError as RootOsError};
-use crate::event_loop::{AsyncRequestSerial, ControlFlow, DeviceEvents, EventLoopClosed};
+use crate::event_loop::{
+    ActiveEventLoop as RootELW, AsyncRequestSerial, ControlFlow, DeviceEvents, EventLoopClosed,
+};
 use crate::icon::Icon;
 use crate::keyboard::Key;
+use crate::platform::pump_events::PumpStatus;
 #[cfg(x11_platform)]
 use crate::platform::x11::{WindowType as XWindowType, XlibErrorHook};
 use crate::window::{
@@ -798,23 +799,25 @@ impl<T: 'static> EventLoop<T> {
         x11_or_wayland!(match self; EventLoop(evlp) => evlp.create_proxy(); as EventLoopProxy)
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(self, app: &mut A) -> Result<(), EventLoopError> {
-        x11_or_wayland!(match self; EventLoop(evlp) => evlp.run_app(app))
+    pub fn run<F>(mut self, callback: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(crate::event::Event<T>, &RootELW),
+    {
+        self.run_on_demand(callback)
     }
 
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
-        x11_or_wayland!(match self; EventLoop(evlp) => evlp.run_app_on_demand(app))
+    pub fn run_on_demand<F>(&mut self, callback: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(crate::event::Event<T>, &RootELW),
+    {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.run_on_demand(callback))
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
-        x11_or_wayland!(match self; EventLoop(evlp) => evlp.pump_app_events(timeout, app))
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, callback: F) -> PumpStatus
+    where
+        F: FnMut(crate::event::Event<T>, &RootELW),
+    {
+        x11_or_wayland!(match self; EventLoop(evlp) => evlp.pump_events(timeout, callback))
     }
 
     pub fn window_target(&self) -> &crate::event_loop::ActiveEventLoop {

src/platform_impl/linux/wayland/event_loop/mod.rs

@@ -14,7 +14,6 @@ use sctk::reexports::calloop::Error as CalloopError;
 use sctk::reexports::calloop_wayland_source::WaylandSource;
 use sctk::reexports::client::{globals, Connection, QueueHandle};
 
-use crate::application::ApplicationHandler;
 use crate::cursor::OnlyCursorImage;
 use crate::dpi::LogicalSize;
 use crate::error::{EventLoopError, OsError as RootOsError};
@@ -174,16 +173,12 @@ impl<T: 'static> EventLoop<T> {
         Ok(event_loop)
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
-        self.run_app_on_demand(app)
-    }
-
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
+    pub fn run_on_demand<F>(&mut self, mut event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         let exit = loop {
-            match self.pump_app_events(None, app) {
+            match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {
                     break Ok(());
                 },
@@ -205,27 +200,26 @@ impl<T: 'static> EventLoop<T> {
         exit
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, mut callback: F) -> PumpStatus
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         if !self.loop_running {
             self.loop_running = true;
 
             // Run the initial loop iteration.
-            self.single_iteration(app, StartCause::Init);
+            self.single_iteration(&mut callback, StartCause::Init);
         }
 
         // Consider the possibility that the `StartCause::Init` iteration could
         // request to Exit.
         if !self.exiting() {
-            self.poll_events_with_timeout(timeout, app);
+            self.poll_events_with_timeout(timeout, &mut callback);
         }
         if let Some(code) = self.exit_code() {
             self.loop_running = false;
 
-            app.exiting(&self.window_target);
+            callback(Event::LoopExiting, self.window_target());
 
             PumpStatus::Exit(code)
         } else {
@@ -233,11 +227,10 @@ impl<T: 'static> EventLoop<T> {
         }
     }
 
-    pub fn poll_events_with_timeout<A: ApplicationHandler<T>>(
-        &mut self,
-        mut timeout: Option<Duration>,
-        app: &mut A,
-    ) {
+    pub fn poll_events_with_timeout<F>(&mut self, mut timeout: Option<Duration>, mut callback: F)
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         let cause = loop {
             let start = Instant::now();
 
@@ -299,10 +292,13 @@ impl<T: 'static> EventLoop<T> {
             break cause;
         };
 
-        self.single_iteration(app, cause);
+        self.single_iteration(&mut callback, cause);
     }
 
-    fn single_iteration<A: ApplicationHandler<T>>(&mut self, app: &mut A, cause: StartCause) {
+    fn single_iteration<F>(&mut self, callback: &mut F, cause: StartCause)
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         // NOTE currently just indented to simplify the diff
 
         // We retain these grow-only scratch buffers as part of the EventLoop
@@ -313,18 +309,18 @@ impl<T: 'static> EventLoop<T> {
         let mut buffer_sink = std::mem::take(&mut self.buffer_sink);
         let mut window_ids = std::mem::take(&mut self.window_ids);
 
-        app.new_events(&self.window_target, cause);
+        callback(Event::NewEvents(cause), &self.window_target);
 
         // NB: For consistency all platforms must emit a 'resumed' event even though Wayland
         // applications don't themselves have a formal suspend/resume lifecycle.
         if cause == StartCause::Init {
-            app.resumed(&self.window_target);
+            callback(Event::Resumed, &self.window_target);
         }
 
         // Handle pending user events. We don't need back buffer, since we can't dispatch
         // user events indirectly via callback to the user.
         for user_event in self.pending_user_events.borrow_mut().drain(..) {
-            app.user_event(&self.window_target, user_event);
+            callback(Event::UserEvent(user_event), &self.window_target);
         }
 
         // Drain the pending compositor updates.
@@ -345,13 +341,18 @@ impl<T: 'static> EventLoop<T> {
                 let old_physical_size = physical_size;
 
                 let new_inner_size = Arc::new(Mutex::new(physical_size));
-                let root_window_id = crate::window::WindowId(window_id);
-                let event = WindowEvent::ScaleFactorChanged {
-                    scale_factor,
-                    inner_size_writer: InnerSizeWriter::new(Arc::downgrade(&new_inner_size)),
-                };
-
-                app.window_event(&self.window_target, root_window_id, event);
+                callback(
+                    Event::WindowEvent {
+                        window_id: crate::window::WindowId(window_id),
+                        event: WindowEvent::ScaleFactorChanged {
+                            scale_factor,
+                            inner_size_writer: InnerSizeWriter::new(Arc::downgrade(
+                                &new_inner_size,
+                            )),
+                        },
+                    },
+                    &self.window_target,
+                );
 
                 let physical_size = *new_inner_size.lock().unwrap();
                 drop(new_inner_size);
@@ -394,14 +395,23 @@ impl<T: 'static> EventLoop<T> {
                     size
                 });
 
-                let window_id = crate::window::WindowId(window_id);
-                let event = WindowEvent::Resized(physical_size);
-                app.window_event(&self.window_target, window_id, event);
+                callback(
+                    Event::WindowEvent {
+                        window_id: crate::window::WindowId(window_id),
+                        event: WindowEvent::Resized(physical_size),
+                    },
+                    &self.window_target,
+                );
             }
 
             if compositor_update.close_window {
-                let window_id = crate::window::WindowId(window_id);
-                app.window_event(&self.window_target, window_id, WindowEvent::CloseRequested);
+                callback(
+                    Event::WindowEvent {
+                        window_id: crate::window::WindowId(window_id),
+                        event: WindowEvent::CloseRequested,
+                    },
+                    &self.window_target,
+                );
             }
         }
 
@@ -410,15 +420,8 @@ impl<T: 'static> EventLoop<T> {
             buffer_sink.append(&mut state.window_events_sink.lock().unwrap());
         });
         for event in buffer_sink.drain() {
-            match event {
-                Event::WindowEvent { window_id, event } => {
-                    app.window_event(&self.window_target, window_id, event)
-                },
-                Event::DeviceEvent { device_id, event } => {
-                    app.device_event(&self.window_target, device_id, event)
-                },
-                _ => unreachable!("event which is neither device nor window event."),
-            }
+            let event = event.map_nonuser_event().unwrap();
+            callback(event, &self.window_target);
         }
 
         // Handle non-synthetic events.
@@ -426,15 +429,8 @@ impl<T: 'static> EventLoop<T> {
             buffer_sink.append(&mut state.events_sink);
         });
         for event in buffer_sink.drain() {
-            match event {
-                Event::WindowEvent { window_id, event } => {
-                    app.window_event(&self.window_target, window_id, event)
-                },
-                Event::DeviceEvent { device_id, event } => {
-                    app.device_event(&self.window_target, device_id, event)
-                },
-                _ => unreachable!("event which is neither device nor window event."),
-            }
+            let event = event.map_nonuser_event().unwrap();
+            callback(event, &self.window_target);
         }
 
         // Collect the window ids
@@ -470,8 +466,10 @@ impl<T: 'static> EventLoop<T> {
             });
 
             if let Some(event) = event {
-                let window_id = crate::window::WindowId(*window_id);
-                app.window_event(&self.window_target, window_id, event);
+                callback(
+                    Event::WindowEvent { window_id: crate::window::WindowId(*window_id), event },
+                    &self.window_target,
+                );
             }
         }
 
@@ -481,7 +479,7 @@ impl<T: 'static> EventLoop<T> {
         });
 
         // This is always the last event we dispatch before poll again
-        app.about_to_wait(&self.window_target);
+        callback(Event::AboutToWait, &self.window_target);
 
         // Update the window frames and schedule redraws.
         let mut wake_up = false;

src/platform_impl/linux/wayland/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(wayland_platform)]
-
 //! Winit's Wayland backend.
 
 use std::fmt::Display;

src/platform_impl/linux/x11/event_processor.rs

@@ -434,7 +434,7 @@ impl EventProcessor {
             let flags = xev.data.get_long(1);
             let version = flags >> 24;
             self.dnd.version = Some(version);
-            let has_more_types = flags - (flags & (c_long::max_value() - 1)) == 1;
+            let has_more_types = flags - (flags & (c_long::MAX - 1)) == 1;
             if !has_more_types {
                 let type_list = vec![
                     xev.data.get_long(2) as xproto::Atom,

src/platform_impl/linux/x11/ime/context.rs

@@ -158,7 +158,9 @@ struct PreeditCallbacks {
 impl PreeditCallbacks {
     pub fn new(client_data: ffi::XPointer) -> PreeditCallbacks {
         let start_callback = create_xim_callback(client_data, unsafe {
-            mem::transmute(preedit_start_callback as usize)
+            mem::transmute::<usize, unsafe extern "C" fn(ffi::XIM, ffi::XPointer, ffi::XPointer)>(
+                preedit_start_callback as usize,
+            )
         });
         let done_callback = create_xim_callback(client_data, preedit_done_callback);
         let caret_callback = create_xim_callback(client_data, preedit_caret_callback);

src/platform_impl/linux/x11/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(x11_platform)]
-
 use std::cell::{Cell, RefCell};
 use std::collections::{HashMap, HashSet, VecDeque};
 use std::ffi::CStr;
@@ -27,7 +25,6 @@ use x11rb::protocol::xproto::{self, ConnectionExt as _};
 use x11rb::x11_utils::X11Error as LogicalError;
 use x11rb::xcb_ffi::ReplyOrIdError;
 
-use crate::application::ApplicationHandler;
 use crate::error::{EventLoopError, OsError as RootOsError};
 use crate::event::{Event, StartCause, WindowEvent};
 use crate::event_loop::{ActiveEventLoop as RootAEL, ControlFlow, DeviceEvents, EventLoopClosed};
@@ -380,16 +377,12 @@ impl<T: 'static> EventLoop<T> {
         &self.event_processor.target
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
-        self.run_app_on_demand(app)
-    }
-
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
+    pub fn run_on_demand<F>(&mut self, mut event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         let exit = loop {
-            match self.pump_app_events(None, app) {
+            match self.pump_events(None, &mut event_handler) {
                 PumpStatus::Exit(0) => {
                     break Ok(());
                 },
@@ -414,27 +407,26 @@ impl<T: 'static> EventLoop<T> {
         exit
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, mut callback: F) -> PumpStatus
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         if !self.loop_running {
             self.loop_running = true;
 
             // run the initial loop iteration
-            self.single_iteration(app, StartCause::Init);
+            self.single_iteration(&mut callback, StartCause::Init);
         }
 
         // Consider the possibility that the `StartCause::Init` iteration could
         // request to Exit.
         if !self.exiting() {
-            self.poll_events_with_timeout(timeout, app);
+            self.poll_events_with_timeout(timeout, &mut callback);
         }
         if let Some(code) = self.exit_code() {
             self.loop_running = false;
 
-            app.exiting(self.window_target());
+            callback(Event::LoopExiting, self.window_target());
 
             PumpStatus::Exit(code)
         } else {
@@ -448,11 +440,10 @@ impl<T: 'static> EventLoop<T> {
             || self.redraw_receiver.has_incoming()
     }
 
-    pub fn poll_events_with_timeout<A: ApplicationHandler<T>>(
-        &mut self,
-        mut timeout: Option<Duration>,
-        app: &mut A,
-    ) {
+    pub fn poll_events_with_timeout<F>(&mut self, mut timeout: Option<Duration>, mut callback: F)
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         let start = Instant::now();
 
         let has_pending = self.has_pending();
@@ -510,20 +501,23 @@ impl<T: 'static> EventLoop<T> {
             return;
         }
 
-        self.single_iteration(app, cause);
+        self.single_iteration(&mut callback, cause);
     }
 
-    fn single_iteration<A: ApplicationHandler<T>>(&mut self, app: &mut A, cause: StartCause) {
-        app.new_events(&self.event_processor.target, cause);
+    fn single_iteration<F>(&mut self, callback: &mut F, cause: StartCause)
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
+        callback(Event::NewEvents(cause), &self.event_processor.target);
 
         // NB: For consistency all platforms must emit a 'resumed' event even though X11
         // applications don't themselves have a formal suspend/resume lifecycle.
         if cause == StartCause::Init {
-            app.resumed(&self.event_processor.target)
+            callback(Event::Resumed, &self.event_processor.target);
         }
 
         // Process all pending events
-        self.drain_events(app);
+        self.drain_events(callback);
 
         // Empty activation tokens.
         while let Ok((window_id, serial)) = self.activation_receiver.try_recv() {
@@ -533,12 +527,14 @@ impl<T: 'static> EventLoop<T> {
 
             match token {
                 Some(Ok(token)) => {
-                    let window_id = crate::window::WindowId(window_id);
-                    let event = WindowEvent::ActivationTokenDone {
-                        serial,
-                        token: crate::window::ActivationToken::_new(token),
+                    let event = Event::WindowEvent {
+                        window_id: crate::window::WindowId(window_id),
+                        event: WindowEvent::ActivationTokenDone {
+                            serial,
+                            token: crate::window::ActivationToken::_new(token),
+                        },
                     };
-                    app.window_event(&self.event_processor.target, window_id, event);
+                    callback(event, &self.event_processor.target)
                 },
                 Some(Err(e)) => {
                     tracing::error!("Failed to get activation token: {}", e);
@@ -550,7 +546,7 @@ impl<T: 'static> EventLoop<T> {
         // Empty the user event buffer
         {
             while let Ok(event) = self.user_receiver.try_recv() {
-                app.user_event(&self.event_processor.target, event);
+                callback(Event::UserEvent(event), &self.event_processor.target);
             }
         }
 
@@ -564,24 +560,28 @@ impl<T: 'static> EventLoop<T> {
 
             for window_id in windows {
                 let window_id = crate::window::WindowId(window_id);
-                app.window_event(
+                callback(
+                    Event::WindowEvent { window_id, event: WindowEvent::RedrawRequested },
                     &self.event_processor.target,
-                    window_id,
-                    WindowEvent::RedrawRequested,
                 );
             }
         }
 
         // This is always the last event we dispatch before poll again
-        app.about_to_wait(&self.event_processor.target);
+        {
+            callback(Event::AboutToWait, &self.event_processor.target);
+        }
     }
 
-    fn drain_events<A: ApplicationHandler<T>>(&mut self, app: &mut A) {
+    fn drain_events<F>(&mut self, callback: &mut F)
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         let mut xev = MaybeUninit::uninit();
 
         while unsafe { self.event_processor.poll_one_event(xev.as_mut_ptr()) } {
             let mut xev = unsafe { xev.assume_init() };
-            self.event_processor.process_event(&mut xev, |window_target, event: Event<T>| {
+            self.event_processor.process_event(&mut xev, |window_target, event| {
                 if let Event::WindowEvent {
                     window_id: crate::window::WindowId(wid),
                     event: WindowEvent::RedrawRequested,
@@ -590,15 +590,7 @@ impl<T: 'static> EventLoop<T> {
                     let window_target = EventProcessor::window_target(window_target);
                     window_target.redraw_sender.send(wid).unwrap();
                 } else {
-                    match event {
-                        Event::WindowEvent { window_id, event } => {
-                            app.window_event(window_target, window_id, event)
-                        },
-                        Event::DeviceEvent { device_id, event } => {
-                            app.device_event(window_target, device_id, event)
-                        },
-                        _ => unreachable!("event which is neither device nor window event."),
-                    }
+                    callback(event, window_target);
                 }
             });
         }

src/platform_impl/macos/app.rs

@@ -4,7 +4,7 @@ use objc2::{declare_class, msg_send, mutability, ClassType, DeclaredClass};
 use objc2_app_kit::{NSApplication, NSEvent, NSEventModifierFlags, NSEventType, NSResponder};
 use objc2_foundation::{MainThreadMarker, NSObject};
 
-use super::app_delegate::ApplicationDelegate;
+use super::app_state::ApplicationDelegate;
 use crate::event::{DeviceEvent, ElementState};
 
 declare_class!(
@@ -57,25 +57,27 @@ fn maybe_dispatch_device_event(delegate: &ApplicationDelegate, event: &NSEvent)
             let delta_y = unsafe { event.deltaY() } as f64;
 
             if delta_x != 0.0 {
-                delegate.queue_device_event(DeviceEvent::Motion { axis: 0, value: delta_x });
+                delegate.maybe_queue_device_event(DeviceEvent::Motion { axis: 0, value: delta_x });
             }
 
             if delta_y != 0.0 {
-                delegate.queue_device_event(DeviceEvent::Motion { axis: 1, value: delta_y })
+                delegate.maybe_queue_device_event(DeviceEvent::Motion { axis: 1, value: delta_y })
             }
 
             if delta_x != 0.0 || delta_y != 0.0 {
-                delegate.queue_device_event(DeviceEvent::MouseMotion { delta: (delta_x, delta_y) });
+                delegate.maybe_queue_device_event(DeviceEvent::MouseMotion {
+                    delta: (delta_x, delta_y),
+                });
             }
         },
         NSEventType::LeftMouseDown | NSEventType::RightMouseDown | NSEventType::OtherMouseDown => {
-            delegate.queue_device_event(DeviceEvent::Button {
+            delegate.maybe_queue_device_event(DeviceEvent::Button {
                 button: unsafe { event.buttonNumber() } as u32,
                 state: ElementState::Pressed,
             });
         },
         NSEventType::LeftMouseUp | NSEventType::RightMouseUp | NSEventType::OtherMouseUp => {
-            delegate.queue_device_event(DeviceEvent::Button {
+            delegate.maybe_queue_device_event(DeviceEvent::Button {
                 button: unsafe { event.buttonNumber() } as u32,
                 state: ElementState::Released,
             });

src/platform_impl/macos/app_state.rs

@@ -1,40 +1,27 @@
 use std::cell::{Cell, RefCell};
-use std::collections::VecDeque;
 use std::mem;
 use std::rc::Weak;
-use std::sync::{Arc, Mutex};
 use std::time::Instant;
 
 use objc2::rc::Retained;
-use objc2::runtime::AnyObject;
 use objc2::{declare_class, msg_send_id, mutability, ClassType, DeclaredClass};
 use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy, NSApplicationDelegate};
-use objc2_foundation::{MainThreadMarker, NSObject, NSObjectProtocol, NSSize};
+use objc2_foundation::{MainThreadMarker, NSNotification, NSObject, NSObjectProtocol};
 
 use super::event_handler::EventHandler;
 use super::event_loop::{stop_app_immediately, ActiveEventLoop, PanicInfo};
 use super::observer::{EventLoopWaker, RunLoop};
-use super::window::WinitWindow;
 use super::{menu, WindowId, DEVICE_ID};
-use crate::dpi::PhysicalSize;
-use crate::event::{DeviceEvent, Event, InnerSizeWriter, StartCause, WindowEvent};
+use crate::event::{DeviceEvent, Event, StartCause, WindowEvent};
 use crate::event_loop::{ActiveEventLoop as RootActiveEventLoop, ControlFlow};
 use crate::window::WindowId as RootWindowId;
 
 #[derive(Debug)]
-struct Policy(NSApplicationActivationPolicy);
-
-impl Default for Policy {
-    fn default() -> Self {
-        Self(NSApplicationActivationPolicy::Regular)
-    }
-}
-
-#[derive(Debug, Default)]
-pub(super) struct State {
-    activation_policy: Policy,
+pub(super) struct AppState {
+    activation_policy: NSApplicationActivationPolicy,
     default_menu: bool,
     activate_ignoring_other_apps: bool,
+    run_loop: RunLoop,
     event_handler: EventHandler,
     stop_on_launch: Cell<bool>,
     stop_before_wait: Cell<bool>,
@@ -50,7 +37,6 @@ pub(super) struct State {
     waker: RefCell<EventLoopWaker>,
     start_time: Cell<Option<Instant>>,
     wait_timeout: Cell<Option<Instant>>,
-    pending_events: RefCell<VecDeque<QueuedEvent>>,
     pending_redraw: RefCell<Vec<WindowId>>,
     // NOTE: This is strongly referenced by our `NSWindowDelegate` and our `NSView` subclass, and
     // as such should be careful to not add fields that, in turn, strongly reference those.
@@ -67,62 +53,20 @@ declare_class!(
     }
 
     impl DeclaredClass for ApplicationDelegate {
-        type Ivars = State;
+        type Ivars = AppState;
     }
 
     unsafe impl NSObjectProtocol for ApplicationDelegate {}
 
     unsafe impl NSApplicationDelegate for ApplicationDelegate {
-        // NOTE: This will, globally, only be run once, no matter how many
-        // `EventLoop`s the user creates.
         #[method(applicationDidFinishLaunching:)]
-        fn did_finish_launching(&self, _sender: Option<&AnyObject>) {
-            trace_scope!("applicationDidFinishLaunching:");
-            self.ivars().is_launched.set(true);
-
-            let mtm = MainThreadMarker::from(self);
-            let app = NSApplication::sharedApplication(mtm);
-            // We need to delay setting the activation policy and activating the app
-            // until `applicationDidFinishLaunching` has been called. Otherwise the
-            // menu bar is initially unresponsive on macOS 10.15.
-            app.setActivationPolicy(self.ivars().activation_policy.0);
-
-            window_activation_hack(&app);
-            #[allow(deprecated)]
-            app.activateIgnoringOtherApps(self.ivars().activate_ignoring_other_apps);
-
-            if self.ivars().default_menu {
-                // The menubar initialization should be before the `NewEvents` event, to allow
-                // overriding of the default menu even if it's created
-                menu::initialize(&app);
-            }
-
-            self.ivars().waker.borrow_mut().start();
-
-            self.set_is_running(true);
-            self.dispatch_init_events();
-
-            // If the application is being launched via `EventLoop::pump_app_events()` then we'll
-            // want to stop the app once it is launched (and return to the external loop)
-            //
-            // In this case we still want to consider Winit's `EventLoop` to be "running",
-            // so we call `start_running()` above.
-            if self.ivars().stop_on_launch.get() {
-                // NOTE: the original idea had been to only stop the underlying `RunLoop`
-                // for the app but that didn't work as expected (`-[NSApplication run]`
-                // effectively ignored the attempt to stop the RunLoop and re-started it).
-                //
-                // So we return from `pump_events` by stopping the application.
-                let app = NSApplication::sharedApplication(mtm);
-                stop_app_immediately(&app);
-            }
+        fn app_did_finish_launching(&self, notification: &NSNotification) {
+            self.did_finish_launching(notification)
         }
 
         #[method(applicationWillTerminate:)]
-        fn will_terminate(&self, _sender: Option<&AnyObject>) {
-            trace_scope!("applicationWillTerminate:");
-            // TODO: Notify every window that it will be destroyed, like done in iOS?
-            self.internal_exit();
+        fn app_will_terminate(&self, notification: &NSNotification) {
+            self.will_terminate(notification)
         }
     }
 );
@@ -134,15 +78,78 @@ impl ApplicationDelegate {
         default_menu: bool,
         activate_ignoring_other_apps: bool,
     ) -> Retained<Self> {
-        let this = mtm.alloc().set_ivars(State {
-            activation_policy: Policy(activation_policy),
+        let this = mtm.alloc().set_ivars(AppState {
+            activation_policy,
             default_menu,
             activate_ignoring_other_apps,
-            ..Default::default()
+            run_loop: RunLoop::main(mtm),
+            event_handler: EventHandler::new(),
+            stop_on_launch: Cell::new(false),
+            stop_before_wait: Cell::new(false),
+            stop_after_wait: Cell::new(false),
+            stop_on_redraw: Cell::new(false),
+            is_launched: Cell::new(false),
+            is_running: Cell::new(false),
+            exit: Cell::new(false),
+            control_flow: Cell::new(ControlFlow::default()),
+            waker: RefCell::new(EventLoopWaker::new()),
+            start_time: Cell::new(None),
+            wait_timeout: Cell::new(None),
+            pending_redraw: RefCell::new(vec![]),
         });
         unsafe { msg_send_id![super(this), init] }
     }
 
+    // NOTE: This will, globally, only be run once, no matter how many
+    // `EventLoop`s the user creates.
+    fn did_finish_launching(&self, _notification: &NSNotification) {
+        trace_scope!("applicationDidFinishLaunching:");
+        self.ivars().is_launched.set(true);
+
+        let mtm = MainThreadMarker::from(self);
+        let app = NSApplication::sharedApplication(mtm);
+        // We need to delay setting the activation policy and activating the app
+        // until `applicationDidFinishLaunching` has been called. Otherwise the
+        // menu bar is initially unresponsive on macOS 10.15.
+        app.setActivationPolicy(self.ivars().activation_policy);
+
+        window_activation_hack(&app);
+        #[allow(deprecated)]
+        app.activateIgnoringOtherApps(self.ivars().activate_ignoring_other_apps);
+
+        if self.ivars().default_menu {
+            // The menubar initialization should be before the `NewEvents` event, to allow
+            // overriding of the default menu even if it's created
+            menu::initialize(&app);
+        }
+
+        self.ivars().waker.borrow_mut().start();
+
+        self.set_is_running(true);
+        self.dispatch_init_events();
+
+        // If the application is being launched via `EventLoop::pump_app_events()` then we'll
+        // want to stop the app once it is launched (and return to the external loop)
+        //
+        // In this case we still want to consider Winit's `EventLoop` to be "running",
+        // so we call `start_running()` above.
+        if self.ivars().stop_on_launch.get() {
+            // NOTE: the original idea had been to only stop the underlying `RunLoop`
+            // for the app but that didn't work as expected (`-[NSApplication run]`
+            // effectively ignored the attempt to stop the RunLoop and re-started it).
+            //
+            // So we return from `pump_events` by stopping the application.
+            let app = NSApplication::sharedApplication(mtm);
+            stop_app_immediately(&app);
+        }
+    }
+
+    fn will_terminate(&self, _notification: &NSNotification) {
+        trace_scope!("applicationWillTerminate:");
+        // TODO: Notify every window that it will be destroyed, like done in iOS?
+        self.internal_exit();
+    }
+
     pub fn get(mtm: MainThreadMarker) -> Retained<Self> {
         let app = NSApplication::sharedApplication(mtm);
         let delegate =
@@ -193,7 +200,6 @@ impl ApplicationDelegate {
     /// NOTE: that if the `NSApplication` has been launched then that state is preserved,
     /// and we won't need to re-launch the app if subsequent EventLoops are run.
     pub fn internal_exit(&self) {
-        self.handle_event(Event::Suspended);
         self.handle_event(Event::LoopExiting);
 
         self.set_is_running(false);
@@ -235,28 +241,16 @@ impl ApplicationDelegate {
         self.ivars().control_flow.get()
     }
 
-    pub fn queue_window_event(&self, window_id: WindowId, event: WindowEvent) {
-        self.ivars()
-            .pending_events
-            .borrow_mut()
-            .push_back(QueuedEvent::WindowEvent(window_id, event));
+    pub fn maybe_queue_window_event(&self, window_id: WindowId, event: WindowEvent) {
+        self.maybe_queue_event(Event::WindowEvent { window_id: RootWindowId(window_id), event });
     }
 
-    pub fn queue_device_event(&self, event: DeviceEvent) {
-        self.ivars().pending_events.borrow_mut().push_back(QueuedEvent::DeviceEvent(event));
+    pub fn handle_window_event(&self, window_id: WindowId, event: WindowEvent) {
+        self.handle_event(Event::WindowEvent { window_id: RootWindowId(window_id), event });
     }
 
-    pub fn queue_static_scale_factor_changed_event(
-        &self,
-        window: Retained<WinitWindow>,
-        suggested_size: PhysicalSize<u32>,
-        scale_factor: f64,
-    ) {
-        self.ivars().pending_events.borrow_mut().push_back(QueuedEvent::ScaleFactorChanged {
-            window,
-            suggested_size,
-            scale_factor,
-        });
+    pub fn maybe_queue_device_event(&self, event: DeviceEvent) {
+        self.maybe_queue_event(Event::DeviceEvent { device_id: DEVICE_ID, event });
     }
 
     pub fn handle_redraw(&self, window_id: WindowId) {
@@ -284,9 +278,27 @@ impl ApplicationDelegate {
         if !pending_redraw.contains(&window_id) {
             pending_redraw.push(window_id);
         }
-        unsafe { RunLoop::get() }.wakeup();
+        self.ivars().run_loop.wakeup();
     }
 
+    #[track_caller]
+    fn maybe_queue_event(&self, event: Event<HandlePendingUserEvents>) {
+        // Most programmer actions in AppKit (e.g. change window fullscreen, set focused, etc.)
+        // result in an event being queued, and applied at a later point.
+        //
+        // However, it is not documented which actions do this, and which ones are done immediately,
+        // so to make sure that we don't encounter re-entrancy issues, we first check if we're
+        // currently handling another event, and if we are, we queue the event instead.
+        if !self.ivars().event_handler.in_use() {
+            self.handle_event(event);
+        } else {
+            tracing::debug!(?event, "had to queue event since another is currently being handled");
+            let this = self.retain();
+            self.ivars().run_loop.queue_closure(move || this.handle_event(event));
+        }
+    }
+
+    #[track_caller]
     fn handle_event(&self, event: Event<HandlePendingUserEvents>) {
         self.ivars().event_handler.handle_event(event, &ActiveEventLoop::new_root(self.retain()))
     }
@@ -348,49 +360,6 @@ impl ApplicationDelegate {
 
         self.handle_event(Event::UserEvent(HandlePendingUserEvents));
 
-        let events = mem::take(&mut *self.ivars().pending_events.borrow_mut());
-        for event in events {
-            match event {
-                QueuedEvent::WindowEvent(window_id, event) => {
-                    self.handle_event(Event::WindowEvent {
-                        window_id: RootWindowId(window_id),
-                        event,
-                    });
-                },
-                QueuedEvent::DeviceEvent(event) => {
-                    self.handle_event(Event::DeviceEvent { device_id: DEVICE_ID, event });
-                },
-                QueuedEvent::ScaleFactorChanged { window, suggested_size, scale_factor } => {
-                    let new_inner_size = Arc::new(Mutex::new(suggested_size));
-                    let scale_factor_changed_event = Event::WindowEvent {
-                        window_id: RootWindowId(window.id()),
-                        event: WindowEvent::ScaleFactorChanged {
-                            scale_factor,
-                            inner_size_writer: InnerSizeWriter::new(Arc::downgrade(
-                                &new_inner_size,
-                            )),
-                        },
-                    };
-
-                    self.handle_event(scale_factor_changed_event);
-
-                    let physical_size = *new_inner_size.lock().unwrap();
-                    drop(new_inner_size);
-                    if physical_size != suggested_size {
-                        let logical_size = physical_size.to_logical(scale_factor);
-                        let size = NSSize::new(logical_size.width, logical_size.height);
-                        window.setContentSize(size);
-                    }
-
-                    let resized_event = Event::WindowEvent {
-                        window_id: RootWindowId(window.id()),
-                        event: WindowEvent::Resized(physical_size),
-                    };
-                    self.handle_event(resized_event);
-                },
-            }
-        }
-
         let redraw = mem::take(&mut *self.ivars().pending_redraw.borrow_mut());
         for window_id in redraw {
             self.handle_event(Event::WindowEvent {
@@ -421,17 +390,6 @@ impl ApplicationDelegate {
     }
 }
 
-#[derive(Debug)]
-pub(crate) enum QueuedEvent {
-    WindowEvent(WindowId, WindowEvent),
-    DeviceEvent(DeviceEvent),
-    ScaleFactorChanged {
-        window: Retained<WinitWindow>,
-        suggested_size: PhysicalSize<u32>,
-        scale_factor: f64,
-    },
-}
-
 #[derive(Debug)]
 pub(crate) struct HandlePendingUserEvents;
 

src/platform_impl/macos/event_handler.rs

@@ -1,7 +1,7 @@
 use std::cell::RefCell;
 use std::{fmt, mem};
 
-use super::app_delegate::HandlePendingUserEvents;
+use super::app_state::HandlePendingUserEvents;
 use crate::event::Event;
 use crate::event_loop::ActiveEventLoop as RootActiveEventLoop;
 
@@ -16,7 +16,7 @@ impl fmt::Debug for EventHandlerData {
     }
 }
 
-#[derive(Debug, Default)]
+#[derive(Debug)]
 pub(crate) struct EventHandler {
     /// This can be in the following states:
     /// - Not registered by the event loop (None).
@@ -26,6 +26,10 @@ pub(crate) struct EventHandler {
 }
 
 impl EventHandler {
+    pub(crate) const fn new() -> Self {
+        Self { inner: RefCell::new(None) }
+    }
+
     /// Set the event loop handler for the duration of the given closure.
     ///
     /// This is similar to using the `scoped-tls` or `scoped-tls-hkt` crates

src/platform_impl/macos/event_loop.rs

@@ -21,11 +21,10 @@ use objc2_app_kit::{NSApplication, NSApplicationActivationPolicy, NSWindow};
 use objc2_foundation::{MainThreadMarker, NSObjectProtocol};
 
 use super::app::WinitApplication;
-use super::app_delegate::{ApplicationDelegate, HandlePendingUserEvents};
+use super::app_state::{ApplicationDelegate, HandlePendingUserEvents};
 use super::event::dummy_event;
 use super::monitor::{self, MonitorHandle};
 use super::observer::setup_control_flow_observers;
-use crate::application::ApplicationHandler;
 use crate::error::EventLoopError;
 use crate::event::Event;
 use crate::event_loop::{
@@ -156,28 +155,17 @@ impl ActiveEventLoop {
     }
 }
 
-fn map_user_event<T: 'static, A: ApplicationHandler<T>>(
-    app: &mut A,
+fn map_user_event<T: 'static>(
+    mut handler: impl FnMut(Event<T>, &RootWindowTarget),
     receiver: Rc<mpsc::Receiver<T>>,
-) -> impl FnMut(Event<HandlePendingUserEvents>, &RootWindowTarget) + '_ {
-    move |event, window_target| match event {
-        Event::NewEvents(cause) => app.new_events(window_target, cause),
-        Event::WindowEvent { window_id, event } => {
-            app.window_event(window_target, window_id, event)
-        },
-        Event::DeviceEvent { device_id, event } => {
-            app.device_event(window_target, device_id, event)
-        },
-        Event::UserEvent(_) => {
+) -> impl FnMut(Event<HandlePendingUserEvents>, &RootWindowTarget) {
+    move |event, window_target| match event.map_nonuser_event() {
+        Ok(event) => (handler)(event, window_target),
+        Err(_) => {
             for event in receiver.try_iter() {
-                app.user_event(window_target, event);
+                (handler)(Event::UserEvent(event), window_target);
             }
         },
-        Event::Suspended => app.suspended(window_target),
-        Event::Resumed => app.resumed(window_target),
-        Event::AboutToWait => app.about_to_wait(window_target),
-        Event::LoopExiting => app.exiting(window_target),
-        Event::MemoryWarning => app.memory_warning(window_target),
     }
 }
 
@@ -252,7 +240,7 @@ impl<T> EventLoop<T> {
         });
 
         let panic_info: Rc<PanicInfo> = Default::default();
-        setup_control_flow_observers(Rc::downgrade(&panic_info));
+        setup_control_flow_observers(mtm, Rc::downgrade(&panic_info));
 
         let (sender, receiver) = mpsc::channel();
         Ok(EventLoop {
@@ -272,19 +260,22 @@ impl<T> EventLoop<T> {
         &self.window_target
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
-        self.run_app_on_demand(app)
+    pub fn run<F>(mut self, handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootWindowTarget),
+    {
+        self.run_on_demand(handler)
     }
 
     // NB: we don't base this on `pump_events` because for `MacOs` we can't support
     // `pump_events` elegantly (we just ask to run the loop for a "short" amount of
     // time and so a layered implementation would end up using a lot of CPU due to
     // redundant wake ups.
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
-        let handler = map_user_event(app, self.receiver.clone());
+    pub fn run_on_demand<F>(&mut self, handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootWindowTarget),
+    {
+        let handler = map_user_event(handler, self.receiver.clone());
 
         self.delegate.set_event_handler(handler, || {
             autoreleasepool(|_| {
@@ -319,12 +310,11 @@ impl<T> EventLoop<T> {
         Ok(())
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
-        let handler = map_user_event(app, self.receiver.clone());
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, handler: F) -> PumpStatus
+    where
+        F: FnMut(Event<T>, &RootWindowTarget),
+    {
+        let handler = map_user_event(handler, self.receiver.clone());
 
         self.delegate.set_event_handler(handler, || {
             autoreleasepool(|_| {
@@ -492,8 +482,7 @@ impl<T> EventLoopProxy<T> {
                 cancel: None,
                 perform: event_loop_proxy_handler,
             };
-            let source =
-                CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::max_value() - 1, &mut context);
+            let source = CFRunLoopSourceCreate(ptr::null_mut(), CFIndex::MAX - 1, &mut context);
             CFRunLoopAddSource(rl, source, kCFRunLoopCommonModes);
             CFRunLoopWakeUp(rl);
 

src/platform_impl/macos/mod.rs

@@ -2,7 +2,7 @@
 mod util;
 
 mod app;
-mod app_delegate;
+mod app_state;
 mod cursor;
 mod event;
 mod event_handler;

src/platform_impl/macos/observer.rs

@@ -1,21 +1,28 @@
+//! Utilities for working with `CFRunLoop`.
+//!
+//! See Apple's documentation on Run Loops for details:
+//! <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Multithreading/RunLoopManagement/RunLoopManagement.html>
+use std::cell::Cell;
 use std::ffi::c_void;
 use std::panic::{AssertUnwindSafe, UnwindSafe};
 use std::ptr;
 use std::rc::Weak;
 use std::time::Instant;
 
-use core_foundation::base::{CFIndex, CFOptionFlags, CFRelease};
+use block2::Block;
+use core_foundation::base::{CFIndex, CFOptionFlags, CFRelease, CFTypeRef};
 use core_foundation::date::CFAbsoluteTimeGetCurrent;
 use core_foundation::runloop::{
-    kCFRunLoopAfterWaiting, kCFRunLoopBeforeWaiting, kCFRunLoopCommonModes, kCFRunLoopExit,
-    CFRunLoopActivity, CFRunLoopAddObserver, CFRunLoopAddTimer, CFRunLoopGetMain,
+    kCFRunLoopAfterWaiting, kCFRunLoopBeforeWaiting, kCFRunLoopCommonModes, kCFRunLoopDefaultMode,
+    kCFRunLoopExit, CFRunLoopActivity, CFRunLoopAddObserver, CFRunLoopAddTimer, CFRunLoopGetMain,
     CFRunLoopObserverCallBack, CFRunLoopObserverContext, CFRunLoopObserverCreate,
     CFRunLoopObserverRef, CFRunLoopRef, CFRunLoopTimerCreate, CFRunLoopTimerInvalidate,
     CFRunLoopTimerRef, CFRunLoopTimerSetNextFireDate, CFRunLoopWakeUp,
 };
 use objc2_foundation::MainThreadMarker;
+use tracing::error;
 
-use super::app_delegate::ApplicationDelegate;
+use super::app_state::ApplicationDelegate;
 use super::event_loop::{stop_app_on_panic, PanicInfo};
 use super::ffi;
 
@@ -84,10 +91,20 @@ extern "C" fn control_flow_end_handler(
     }
 }
 
+#[derive(Debug)]
 pub struct RunLoop(CFRunLoopRef);
 
+impl Default for RunLoop {
+    fn default() -> Self {
+        Self(ptr::null_mut())
+    }
+}
+
 impl RunLoop {
-    pub unsafe fn get() -> Self {
+    pub fn main(mtm: MainThreadMarker) -> Self {
+        // SAFETY: We have a MainThreadMarker here, which means we know we're on the main thread, so
+        // scheduling (and scheduling a non-`Send` block) to that thread is allowed.
+        let _ = mtm;
         RunLoop(unsafe { CFRunLoopGetMain() })
     }
 
@@ -114,9 +131,79 @@ impl RunLoop {
         };
         unsafe { CFRunLoopAddObserver(self.0, observer, kCFRunLoopCommonModes) };
     }
+
+    /// Submit a closure to run on the main thread as the next step in the run loop, before other
+    /// event sources are processed.
+    ///
+    /// This is used for running event handlers, as those are not allowed to run re-entrantly.
+    ///
+    /// # Implementation
+    ///
+    /// This queuing could be implemented in the following several ways with subtle differences in
+    /// timing. This list is sorted in rough order in which they are run:
+    ///
+    /// 1. Using `CFRunLoopPerformBlock` or `-[NSRunLoop performBlock:]`.
+    ///
+    /// 2. Using `-[NSObject performSelectorOnMainThread:withObject:waitUntilDone:]` or wrapping the
+    ///    event in `NSEvent` and posting that to `-[NSApplication postEvent:atStart:]` (both
+    ///    creates a custom `CFRunLoopSource`, and signals that to wake up the main event loop).
+    ///
+    ///    a. `atStart = true`.
+    ///
+    ///    b. `atStart = false`.
+    ///
+    /// 3. `dispatch_async` or `dispatch_async_f`. Note that this may appear before 2b, it does not
+    ///    respect the ordering that runloop events have.
+    ///
+    /// We choose the first one, both for ease-of-implementation, but mostly for consistency, as we
+    /// want the event to be queued in a way that preserves the order the events originally arrived
+    /// in.
+    ///
+    /// As an example, let's assume that we receive two events from the user, a mouse click which we
+    /// handled by queuing it, and a window resize which we handled immediately. If we allowed
+    /// AppKit to choose the ordering when queuing the mouse event, it might get put in the back of
+    /// the queue, and the events would appear out of order to the user of Winit. So we must instead
+    /// put the event at the very front of the queue, to be handled as soon as possible after
+    /// handling whatever event it's currently handling.
+    pub fn queue_closure(&self, closure: impl FnOnce() + 'static) {
+        extern "C" {
+            fn CFRunLoopPerformBlock(rl: CFRunLoopRef, mode: CFTypeRef, block: &Block<dyn Fn()>);
+        }
+
+        // Convert `FnOnce()` to `Block<dyn Fn()>`.
+        let closure = Cell::new(Some(closure));
+        let block = block2::RcBlock::new(move || {
+            if let Some(closure) = closure.take() {
+                closure()
+            } else {
+                error!("tried to execute queued closure on main thread twice");
+            }
+        });
+
+        // There are a few common modes (`kCFRunLoopCommonModes`) defined by Cocoa:
+        // - `NSDefaultRunLoopMode`, alias of `kCFRunLoopDefaultMode`.
+        // - `NSEventTrackingRunLoopMode`, used when mouse-dragging and live-resizing a window.
+        // - `NSModalPanelRunLoopMode`, used when running a modal inside the Winit event loop.
+        // - `NSConnectionReplyMode`: TODO.
+        //
+        // We only want to run event handlers in the default mode, as we support running a blocking
+        // modal inside a Winit event handler (see [#1779]) which outrules the modal panel mode, and
+        // resizing such panel window enters the event tracking run loop mode, so we can't directly
+        // trigger events inside that mode either.
+        //
+        // Any events that are queued while running a modal or when live-resizing will instead wait,
+        // and be delivered to the application afterwards.
+        //
+        // [#1779]: https://github.com/rust-windowing/winit/issues/1779
+        let mode = unsafe { kCFRunLoopDefaultMode as CFTypeRef };
+
+        // SAFETY: The runloop is valid, the mode is a `CFStringRef`, and the block is `'static`.
+        unsafe { CFRunLoopPerformBlock(self.0, mode, &block) }
+    }
 }
 
-pub fn setup_control_flow_observers(panic_info: Weak<PanicInfo>) {
+pub fn setup_control_flow_observers(mtm: MainThreadMarker, panic_info: Weak<PanicInfo>) {
+    let run_loop = RunLoop::main(mtm);
     unsafe {
         let mut context = CFRunLoopObserverContext {
             info: Weak::into_raw(panic_info) as *mut _,
@@ -125,16 +212,15 @@ pub fn setup_control_flow_observers(panic_info: Weak<PanicInfo>) {
             release: None,
             copyDescription: None,
         };
-        let run_loop = RunLoop::get();
         run_loop.add_observer(
             kCFRunLoopAfterWaiting,
-            CFIndex::min_value(),
+            CFIndex::MIN,
             control_flow_begin_handler,
             &mut context as *mut _,
         );
         run_loop.add_observer(
             kCFRunLoopExit | kCFRunLoopBeforeWaiting,
-            CFIndex::max_value(),
+            CFIndex::MAX,
             control_flow_end_handler,
             &mut context as *mut _,
         );
@@ -165,8 +251,8 @@ impl Drop for EventLoopWaker {
     }
 }
 
-impl Default for EventLoopWaker {
-    fn default() -> EventLoopWaker {
+impl EventLoopWaker {
+    pub(crate) fn new() -> Self {
         extern "C" fn wakeup_main_loop(_timer: CFRunLoopTimerRef, _info: *mut c_void) {}
         unsafe {
             // Create a timer with a 0.1µs interval (1ns does not work) to mimic polling.
@@ -174,7 +260,7 @@ impl Default for EventLoopWaker {
             // future, but that gets changed to fire immediately in did_finish_launching
             let timer = CFRunLoopTimerCreate(
                 ptr::null_mut(),
-                std::f64::MAX,
+                f64::MAX,
                 0.000_000_1,
                 0,
                 0,
@@ -182,23 +268,21 @@ impl Default for EventLoopWaker {
                 ptr::null_mut(),
             );
             CFRunLoopAddTimer(CFRunLoopGetMain(), timer, kCFRunLoopCommonModes);
-            EventLoopWaker { timer, start_instant: Instant::now(), next_fire_date: None }
+            Self { timer, start_instant: Instant::now(), next_fire_date: None }
         }
     }
-}
 
-impl EventLoopWaker {
     pub fn stop(&mut self) {
         if self.next_fire_date.is_some() {
             self.next_fire_date = None;
-            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MAX) }
+            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MAX) }
         }
     }
 
     pub fn start(&mut self) {
         if self.next_fire_date != Some(self.start_instant) {
             self.next_fire_date = Some(self.start_instant);
-            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, std::f64::MIN) }
+            unsafe { CFRunLoopTimerSetNextFireDate(self.timer, f64::MIN) }
         }
     }
 

src/platform_impl/macos/view.rs

@@ -16,7 +16,7 @@ use objc2_foundation::{
     NSPoint, NSRange, NSRect, NSSize, NSString, NSUInteger,
 };
 
-use super::app_delegate::ApplicationDelegate;
+use super::app_state::ApplicationDelegate;
 use super::cursor::{default_cursor, invisible_cursor};
 use super::event::{
     code_to_key, code_to_location, create_key_event, event_mods, lalt_pressed, ralt_pressed,
@@ -270,19 +270,20 @@ declare_class!(
         fn set_marked_text(
             &self,
             string: &NSObject,
-            _selected_range: NSRange,
+            selected_range: NSRange,
             _replacement_range: NSRange,
         ) {
+            // TODO: Use _replacement_range, requires changing the event to report surrounding text.
             trace_scope!("setMarkedText:selectedRange:replacementRange:");
 
             // SAFETY: This method is guaranteed to get either a `NSString` or a `NSAttributedString`.
-            let (marked_text, preedit_string) = if string.is_kind_of::<NSAttributedString>() {
+            let (marked_text, string) = if string.is_kind_of::<NSAttributedString>() {
                 let string: *const NSObject = string;
                 let string: *const NSAttributedString = string.cast();
                 let string = unsafe { &*string };
                 (
                     NSMutableAttributedString::from_attributed_nsstring(string),
-                    string.string().to_string(),
+                    string.string(),
                 )
             } else {
                 let string: *const NSObject = string;
@@ -290,7 +291,7 @@ declare_class!(
                 let string = unsafe { &*string };
                 (
                     NSMutableAttributedString::from_nsstring(string),
-                    string.to_string(),
+                    string.copy(),
                 )
             };
 
@@ -310,16 +311,21 @@ declare_class!(
                 self.ivars().ime_state.set(ImeState::Ground);
             }
 
-            // Empty string basically means that there's no preedit, so indicate that by sending
-            // `None` cursor range.
-            let cursor_range = if preedit_string.is_empty() {
+            let cursor_range = if string.is_empty() {
+                // An empty string basically means that there's no preedit, so indicate that by
+                // sending a `None` cursor range.
                 None
             } else {
-                Some((preedit_string.len(), preedit_string.len()))
+                // Convert the selected range from UTF-16 indices to UTF-8 indices.
+                let sub_string_a = unsafe { string.substringToIndex(selected_range.location) };
+                let sub_string_b = unsafe { string.substringToIndex(selected_range.end()) };
+                let lowerbound_utf8 = sub_string_a.len();
+                let upperbound_utf8 = sub_string_b.len();
+                Some((lowerbound_utf8, upperbound_utf8))
             };
 
             // Send WindowEvent for updating marked text
-            self.queue_event(WindowEvent::Ime(Ime::Preedit(preedit_string, cursor_range)));
+            self.queue_event(WindowEvent::Ime(Ime::Preedit(string.to_string(), cursor_range)));
         }
 
         #[method(unmarkText)]
@@ -379,6 +385,7 @@ declare_class!(
 
         #[method(insertText:replacementRange:)]
         fn insert_text(&self, string: &NSObject, _replacement_range: NSRange) {
+            // TODO: Use _replacement_range, requires changing the event to report surrounding text.
             trace_scope!("insertText:replacementRange:");
 
             // SAFETY: This method is guaranteed to get either a `NSString` or a `NSAttributedString`.
@@ -679,7 +686,7 @@ declare_class!(
 
             self.update_modifiers(event, false);
 
-            self.queue_device_event(DeviceEvent::MouseWheel { delta });
+            self.ivars().app_delegate.maybe_queue_device_event(DeviceEvent::MouseWheel { delta });
             self.queue_event(WindowEvent::MouseWheel {
                 device_id: DEVICE_ID,
                 delta,
@@ -823,11 +830,7 @@ impl WinitView {
     }
 
     fn queue_event(&self, event: WindowEvent) {
-        self.ivars().app_delegate.queue_window_event(self.window().id(), event);
-    }
-
-    fn queue_device_event(&self, event: DeviceEvent) {
-        self.ivars().app_delegate.queue_device_event(event);
+        self.ivars().app_delegate.maybe_queue_window_event(self.window().id(), event);
     }
 
     fn scale_factor(&self) -> f64 {

src/platform_impl/macos/window_delegate.rs

@@ -1,6 +1,9 @@
 #![allow(clippy::unnecessary_cast)]
 use std::cell::{Cell, RefCell};
 use std::collections::VecDeque;
+use std::ffi::c_void;
+use std::ptr;
+use std::sync::{Arc, Mutex};
 
 use core_graphics::display::{CGDisplay, CGPoint};
 use monitor::VideoModeHandle;
@@ -8,28 +11,31 @@ use objc2::rc::{autoreleasepool, Retained};
 use objc2::runtime::{AnyObject, ProtocolObject};
 use objc2::{declare_class, msg_send_id, mutability, sel, ClassType, DeclaredClass};
 use objc2_app_kit::{
-    NSAppKitVersionNumber, NSAppKitVersionNumber10_12, NSAppearance, NSApplication,
-    NSApplicationPresentationOptions, NSBackingStoreType, NSDraggingDestination,
-    NSFilenamesPboardType, NSPasteboard, NSRequestUserAttentionType, NSScreen, NSView,
-    NSWindowButton, NSWindowDelegate, NSWindowFullScreenButton, NSWindowLevel,
-    NSWindowOcclusionState, NSWindowOrderingMode, NSWindowSharingType, NSWindowStyleMask,
-    NSWindowTabbingMode, NSWindowTitleVisibility,
+    NSAppKitVersionNumber, NSAppKitVersionNumber10_12, NSAppearance, NSAppearanceCustomization,
+    NSAppearanceNameAqua, NSApplication, NSApplicationPresentationOptions, NSBackingStoreType,
+    NSColor, NSDraggingDestination, NSFilenamesPboardType, NSPasteboard,
+    NSRequestUserAttentionType, NSScreen, NSView, NSWindowButton, NSWindowDelegate,
+    NSWindowFullScreenButton, NSWindowLevel, NSWindowOcclusionState, NSWindowOrderingMode,
+    NSWindowSharingType, NSWindowStyleMask, NSWindowTabbingMode, NSWindowTitleVisibility,
 };
 use objc2_foundation::{
-    ns_string, CGFloat, MainThreadMarker, NSArray, NSCopying, NSDistributedNotificationCenter,
-    NSObject, NSObjectNSDelayedPerforming, NSObjectNSThreadPerformAdditions, NSObjectProtocol,
-    NSPoint, NSRect, NSSize, NSString,
+    ns_string, CGFloat, MainThreadMarker, NSArray, NSCopying, NSDictionary, NSKeyValueChangeKey,
+    NSKeyValueChangeNewKey, NSKeyValueChangeOldKey, NSKeyValueObservingOptions, NSObject,
+    NSObjectNSDelayedPerforming, NSObjectNSKeyValueObserverRegistration, NSObjectProtocol, NSPoint,
+    NSRect, NSSize, NSString,
 };
+use tracing::{trace, warn};
 
-use super::app_delegate::ApplicationDelegate;
+use super::app_state::ApplicationDelegate;
 use super::cursor::cursor_from_icon;
 use super::monitor::{self, flip_window_screen_coordinates, get_display_id};
+use super::observer::RunLoop;
 use super::view::WinitView;
 use super::window::WinitWindow;
 use super::{ffi, Fullscreen, MonitorHandle, OsError, WindowId};
 use crate::dpi::{LogicalPosition, LogicalSize, PhysicalPosition, PhysicalSize, Position, Size};
 use crate::error::{ExternalError, NotSupportedError, OsError as RootOsError};
-use crate::event::WindowEvent;
+use crate::event::{InnerSizeWriter, WindowEvent};
 use crate::platform::macos::{OptionAsAlt, WindowExtMacOS};
 use crate::window::{
     Cursor, CursorGrabMode, Icon, ImePurpose, ResizeDirection, Theme, UserAttentionType,
@@ -77,8 +83,6 @@ pub(crate) struct State {
 
     window: Retained<WinitWindow>,
 
-    current_theme: Cell<Option<Theme>>,
-
     // During `windowDidResize`, we use this to only send Moved if the position changed.
     //
     // This is expressed in native screen coordinates.
@@ -184,7 +188,17 @@ declare_class!(
         #[method(windowDidChangeBackingProperties:)]
         fn window_did_change_backing_properties(&self, _: Option<&AnyObject>) {
             trace_scope!("windowDidChangeBackingProperties:");
-            self.queue_static_scale_factor_changed_event();
+            let scale_factor = self.scale_factor();
+            if scale_factor == self.ivars().previous_scale_factor.get() {
+                return;
+            };
+            self.ivars().previous_scale_factor.set(scale_factor);
+
+            let mtm = MainThreadMarker::from(self);
+            let this = self.retain();
+            RunLoop::main(mtm).queue_closure(move || {
+                this.handle_scale_factor_changed(scale_factor);
+            });
         }
 
         #[method(windowDidBecomeKey:)]
@@ -407,32 +421,66 @@ declare_class!(
         }
     }
 
+    // Key-Value Observing
     unsafe impl WindowDelegate {
-        // Observe theme change
-        #[method(effectiveAppearanceDidChange:)]
-        fn effective_appearance_did_change(&self, sender: Option<&AnyObject>) {
-            trace_scope!("effectiveAppearanceDidChange:");
-            unsafe {
-                self.performSelectorOnMainThread_withObject_waitUntilDone(
-                    sel!(effectiveAppearanceDidChangedOnMainThread:),
-                    sender,
-                    false,
-                )
-            };
-        }
+        #[method(observeValueForKeyPath:ofObject:change:context:)]
+        fn observe_value(
+            &self,
+            key_path: Option<&NSString>,
+            _object: Option<&AnyObject>,
+            change: Option<&NSDictionary<NSKeyValueChangeKey, AnyObject>>,
+            _context: *mut c_void,
+        ) {
+            trace_scope!("observeValueForKeyPath:ofObject:change:context:");
+            // NOTE: We don't _really_ need to check the key path, as there should only be one, but
+            // in the future we might want to observe other key paths.
+            if key_path == Some(ns_string!("effectiveAppearance")) {
+                let change = change.expect("requested a change dictionary in `addObserver`, but none was provided");
+                let old = change.get(unsafe { NSKeyValueChangeOldKey }).expect("requested change dictionary did not contain `NSKeyValueChangeOldKey`");
+                let new = change.get(unsafe { NSKeyValueChangeNewKey }).expect("requested change dictionary did not contain `NSKeyValueChangeNewKey`");
 
-        #[method(effectiveAppearanceDidChangedOnMainThread:)]
-        fn effective_appearance_did_changed_on_main_thread(&self, _: Option<&AnyObject>) {
-            let mtm = MainThreadMarker::from(self);
-            let theme = get_ns_theme(mtm);
-            let old_theme = self.ivars().current_theme.replace(Some(theme));
-            if old_theme != Some(theme) {
-                self.queue_event(WindowEvent::ThemeChanged(theme));
+                // SAFETY: The value of `effectiveAppearance` is `NSAppearance`
+                let old: *const AnyObject = old;
+                let old: *const NSAppearance = old.cast();
+                let old: &NSAppearance = unsafe { &*old };
+                let new: *const AnyObject = new;
+                let new: *const NSAppearance = new.cast();
+                let new: &NSAppearance = unsafe { &*new };
+
+                trace!(old = %unsafe { old.name() }, new = %unsafe { new.name() }, "effectiveAppearance changed");
+
+                // Ignore the change if the window's theme is customized by the user (since in that
+                // case the `effectiveAppearance` is only emitted upon said customization, and then
+                // it's triggered directly by a user action, and we don't want to emit the event).
+                if unsafe { self.window().appearance() }.is_some() {
+                    return;
+                }
+
+                let old = appearance_to_theme(old);
+                let new = appearance_to_theme(new);
+                // Check that the theme changed in Winit's terms (the theme might have changed on
+                // other parameters, such as level of contrast, but the event should not be emitted
+                // in those cases).
+                if old == new {
+                    return;
+                }
+
+                self.queue_event(WindowEvent::ThemeChanged(new));
+            } else {
+                panic!("unknown observed keypath {key_path:?}");
             }
         }
     }
 );
 
+impl Drop for WindowDelegate {
+    fn drop(&mut self) {
+        unsafe {
+            self.window().removeObserver_forKeyPath(self, ns_string!("effectiveAppearance"));
+        }
+    }
+}
+
 fn new_window(
     app_delegate: &ApplicationDelegate,
     attrs: &WindowAttributes,
@@ -601,6 +649,8 @@ fn new_window(
 
         if attrs.transparent {
             window.setOpaque(false);
+            // See `set_transparent` for details on why we do this.
+            window.setBackgroundColor(unsafe { Some(&NSColor::clearColor()) });
         }
 
         // register for drag and drop operations.
@@ -654,15 +704,13 @@ impl WindowDelegate {
 
         let scale_factor = window.backingScaleFactor() as _;
 
-        let current_theme = match attrs.preferred_theme {
-            Some(theme) => Some(theme),
-            None => Some(get_ns_theme(mtm)),
-        };
+        if let Some(appearance) = theme_to_appearance(attrs.preferred_theme) {
+            unsafe { window.setAppearance(Some(&appearance)) };
+        }
 
         let delegate = mtm.alloc().set_ivars(State {
             app_delegate: app_delegate.retain(),
             window: window.retain(),
-            current_theme: Cell::new(current_theme),
             previous_position: Cell::new(None),
             previous_scale_factor: Cell::new(scale_factor),
             resize_increments: Cell::new(resize_increments),
@@ -681,18 +729,23 @@ impl WindowDelegate {
         let delegate: Retained<WindowDelegate> = unsafe { msg_send_id![super(delegate), init] };
 
         if scale_factor != 1.0 {
-            delegate.queue_static_scale_factor_changed_event();
+            let delegate = delegate.clone();
+            RunLoop::main(mtm).queue_closure(move || {
+                delegate.handle_scale_factor_changed(scale_factor);
+            });
         }
         window.setDelegate(Some(ProtocolObject::from_ref(&*delegate)));
 
-        // Enable theme change event
-        let notification_center = unsafe { NSDistributedNotificationCenter::defaultCenter() };
+        // Listen for theme change event.
+        //
+        // SAFETY: The observer is un-registered in the `Drop` of the delegate.
         unsafe {
-            notification_center.addObserver_selector_name_object(
+            window.addObserver_forKeyPath_options_context(
                 &delegate,
-                sel!(effectiveAppearanceDidChange:),
-                Some(ns_string!("AppleInterfaceThemeChangedNotification")),
-                None,
+                ns_string!("effectiveAppearance"),
+                NSKeyValueObservingOptions::NSKeyValueObservingOptionNew
+                    | NSKeyValueObservingOptions::NSKeyValueObservingOptionOld,
+                ptr::null_mut(),
             )
         };
 
@@ -754,24 +807,31 @@ impl WindowDelegate {
     }
 
     pub(crate) fn queue_event(&self, event: WindowEvent) {
-        self.ivars().app_delegate.queue_window_event(self.window().id(), event);
+        self.ivars().app_delegate.maybe_queue_window_event(self.window().id(), event);
     }
 
-    fn queue_static_scale_factor_changed_event(&self) {
-        let scale_factor = self.scale_factor();
-        if scale_factor == self.ivars().previous_scale_factor.get() {
-            return;
-        };
+    fn handle_scale_factor_changed(&self, scale_factor: CGFloat) {
+        let app_delegate = &self.ivars().app_delegate;
+        let window = self.window();
 
-        self.ivars().previous_scale_factor.set(scale_factor);
-        let content_size = self.window().contentRectForFrameRect(self.window().frame()).size;
+        let content_size = window.contentRectForFrameRect(window.frame()).size;
         let content_size = LogicalSize::new(content_size.width, content_size.height);
 
-        self.ivars().app_delegate.queue_static_scale_factor_changed_event(
-            self.window().retain(),
-            content_size.to_physical(scale_factor),
+        let suggested_size = content_size.to_physical(scale_factor);
+        let new_inner_size = Arc::new(Mutex::new(suggested_size));
+        app_delegate.handle_window_event(window.id(), WindowEvent::ScaleFactorChanged {
             scale_factor,
-        );
+            inner_size_writer: InnerSizeWriter::new(Arc::downgrade(&new_inner_size)),
+        });
+        let physical_size = *new_inner_size.lock().unwrap();
+        drop(new_inner_size);
+
+        if physical_size != suggested_size {
+            let logical_size = physical_size.to_logical(scale_factor);
+            let size = NSSize::new(logical_size.width, logical_size.height);
+            window.setContentSize(size);
+        }
+        app_delegate.handle_window_event(window.id(), WindowEvent::Resized(physical_size));
     }
 
     fn emit_move_event(&self) {
@@ -799,7 +859,23 @@ impl WindowDelegate {
     }
 
     pub fn set_transparent(&self, transparent: bool) {
-        self.window().setOpaque(!transparent)
+        // This is just a hint for Quartz, it doesn't actually speculate with window alpha.
+        // Providing a wrong value here could result in visual artifacts, when the window is
+        // transparent.
+        self.window().setOpaque(!transparent);
+
+        // AppKit draws the window with a background color by default, which is usually really
+        // nice, but gets in the way when we want to allow the contents of the window to be
+        // transparent, as in that case, the transparent contents will just be drawn on top of
+        // the background color. As such, to allow the window to be transparent, we must also set
+        // the background color to one with an empty alpha channel.
+        let color = if transparent {
+            unsafe { NSColor::clearColor() }
+        } else {
+            unsafe { NSColor::windowBackgroundColor() }
+        };
+
+        self.window().setBackgroundColor(Some(&color));
     }
 
     pub fn set_blur(&self, blur: bool) {
@@ -898,8 +974,8 @@ impl WindowDelegate {
 
     pub fn set_max_inner_size(&self, dimensions: Option<Size>) {
         let dimensions = dimensions.unwrap_or(Size::Logical(LogicalSize {
-            width: std::f32::MAX as f64,
-            height: std::f32::MAX as f64,
+            width: f32::MAX as f64,
+            height: f32::MAX as f64,
         }));
         let scale_factor = self.scale_factor();
         let max_size = dimensions.to_logical::<CGFloat>(scale_factor);
@@ -1575,20 +1651,24 @@ impl WindowDelegate {
         }
     }
 
-    #[inline]
-    pub fn theme(&self) -> Option<Theme> {
-        self.ivars().current_theme.get()
-    }
-
     #[inline]
     pub fn has_focus(&self) -> bool {
         self.window().isKeyWindow()
     }
 
+    pub fn theme(&self) -> Option<Theme> {
+        // Note: We could choose between returning the value of `effectiveAppearance` or
+        // `appearance`, depending on what the user is asking about:
+        // - "how should I render on this particular frame".
+        // - "what is the configuration for this window".
+        //
+        // We choose the latter for consistency with the `set_theme` call, though it might also be
+        // useful to expose the former.
+        Some(appearance_to_theme(unsafe { &*self.window().appearance()? }))
+    }
+
     pub fn set_theme(&self, theme: Option<Theme>) {
-        let mtm = MainThreadMarker::from(self);
-        set_ns_theme(theme, mtm);
-        self.ivars().current_theme.set(theme.or_else(|| Some(get_ns_theme(mtm))));
+        unsafe { self.window().setAppearance(theme_to_appearance(theme).as_deref()) };
     }
 
     #[inline]
@@ -1747,34 +1827,39 @@ impl WindowExtMacOS for WindowDelegate {
 const DEFAULT_STANDARD_FRAME: NSRect =
     NSRect::new(NSPoint::new(50.0, 50.0), NSSize::new(800.0, 600.0));
 
-pub(super) fn get_ns_theme(mtm: MainThreadMarker) -> Theme {
-    let app = NSApplication::sharedApplication(mtm);
-    if !app.respondsToSelector(sel!(effectiveAppearance)) {
-        return Theme::Light;
-    }
-    let appearance = app.effectiveAppearance();
-    let name = appearance
-        .bestMatchFromAppearancesWithNames(&NSArray::from_id_slice(&[
-            NSString::from_str("NSAppearanceNameAqua"),
-            NSString::from_str("NSAppearanceNameDarkAqua"),
-        ]))
-        .unwrap();
-    match &*name.to_string() {
-        "NSAppearanceNameDarkAqua" => Theme::Dark,
-        _ => Theme::Light,
+fn dark_appearance_name() -> &'static NSString {
+    // Don't use the static `NSAppearanceNameDarkAqua` to allow linking on macOS < 10.14
+    ns_string!("NSAppearanceNameDarkAqua")
+}
+
+fn appearance_to_theme(appearance: &NSAppearance) -> Theme {
+    let best_match = appearance.bestMatchFromAppearancesWithNames(&NSArray::from_id_slice(&[
+        unsafe { NSAppearanceNameAqua.copy() },
+        dark_appearance_name().copy(),
+    ]));
+    if let Some(best_match) = best_match {
+        if *best_match == *dark_appearance_name() {
+            Theme::Dark
+        } else {
+            Theme::Light
+        }
+    } else {
+        warn!(?appearance, "failed to determine the theme of the appearance");
+        // Default to light in this case
+        Theme::Light
     }
 }
 
-fn set_ns_theme(theme: Option<Theme>, mtm: MainThreadMarker) {
-    let app = NSApplication::sharedApplication(mtm);
-    if app.respondsToSelector(sel!(effectiveAppearance)) {
-        let appearance = theme.map(|t| {
-            let name = match t {
-                Theme::Dark => NSString::from_str("NSAppearanceNameDarkAqua"),
-                Theme::Light => NSString::from_str("NSAppearanceNameAqua"),
-            };
-            NSAppearance::appearanceNamed(&name).unwrap()
-        });
-        app.setAppearance(appearance.as_ref().map(|a| a.as_ref()));
+fn theme_to_appearance(theme: Option<Theme>) -> Option<Retained<NSAppearance>> {
+    let appearance = match theme? {
+        Theme::Light => unsafe { NSAppearance::appearanceNamed(NSAppearanceNameAqua) },
+        Theme::Dark => NSAppearance::appearanceNamed(dark_appearance_name()),
+    };
+    if let Some(appearance) = appearance {
+        Some(appearance)
+    } else {
+        warn!(?theme, "could not find appearance for theme");
+        // Assume system appearance in this case
+        None
     }
 }

src/platform_impl/orbital/event_loop.rs

@@ -12,7 +12,6 @@ use orbclient::{
 };
 use smol_str::SmolStr;
 
-use crate::application::ApplicationHandler;
 use crate::error::EventLoopError;
 use crate::event::{self, Ime, Modifiers, StartCause};
 use crate::event_loop::{self, ControlFlow, DeviceEvents};
@@ -323,13 +322,14 @@ impl<T: 'static> EventLoop<T> {
         })
     }
 
-    fn process_event<A: ApplicationHandler<T>>(
+    fn process_event<F>(
         window_id: WindowId,
         event_option: EventOption,
         event_state: &mut EventState,
-        window_target: &event_loop::ActiveEventLoop,
-        app: &mut A,
-    ) {
+        mut event_handler: F,
+    ) where
+        F: FnMut(event::Event<T>),
+    {
         match event_option {
             EventOption::Key(KeyEvent { character, scancode, pressed }) => {
                 // Convert scancode
@@ -371,128 +371,125 @@ impl<T: 'static> EventLoop<T> {
                     key_without_modifiers = logical_key.clone();
                 }
 
-                let window_id = RootWindowId(window_id);
-                let event = event::WindowEvent::KeyboardInput {
-                    device_id: event::DeviceId(DeviceId),
-                    event: event::KeyEvent {
-                        logical_key,
-                        physical_key,
-                        location: KeyLocation::Standard,
-                        state: element_state(pressed),
-                        repeat: false,
-                        text,
-                        platform_specific: KeyEventExtra {
-                            key_without_modifiers,
-                            text_with_all_modifiers,
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::KeyboardInput {
+                        device_id: event::DeviceId(DeviceId),
+                        event: event::KeyEvent {
+                            logical_key,
+                            physical_key,
+                            location: KeyLocation::Standard,
+                            state: element_state(pressed),
+                            repeat: false,
+                            text,
+                            platform_specific: KeyEventExtra {
+                                key_without_modifiers,
+                                text_with_all_modifiers,
+                            },
                         },
+                        is_synthetic: false,
                     },
-                    is_synthetic: false,
-                };
-
-                app.window_event(window_target, window_id, event);
+                });
 
                 // If the state of the modifiers has changed, send the event.
                 if modifiers_before != event_state.keyboard {
-                    app.window_event(
-                        window_target,
-                        window_id,
-                        event::WindowEvent::ModifiersChanged(event_state.modifiers()),
-                    );
+                    event_handler(event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::ModifiersChanged(event_state.modifiers()),
+                    })
                 }
             },
             EventOption::TextInput(TextInputEvent { character }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::Ime(Ime::Preedit("".into(), None)),
-                );
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::Ime(Ime::Commit(character.into())),
-                );
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::Ime(Ime::Preedit("".into(), None)),
+                });
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::Ime(Ime::Commit(character.into())),
+                });
             },
             EventOption::Mouse(MouseEvent { x, y }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::CursorMoved {
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::CursorMoved {
                         device_id: event::DeviceId(DeviceId),
                         position: (x, y).into(),
                     },
-                );
+                });
             },
             EventOption::MouseRelative(MouseRelativeEvent { dx, dy }) => {
-                app.device_event(
-                    window_target,
-                    event::DeviceId(DeviceId),
-                    event::DeviceEvent::MouseMotion { delta: (dx as f64, dy as f64) },
-                );
+                event_handler(event::Event::DeviceEvent {
+                    device_id: event::DeviceId(DeviceId),
+                    event: event::DeviceEvent::MouseMotion { delta: (dx as f64, dy as f64) },
+                });
             },
             EventOption::Button(ButtonEvent { left, middle, right }) => {
                 while let Some((button, state)) = event_state.mouse(left, middle, right) {
-                    app.window_event(
-                        window_target,
-                        RootWindowId(window_id),
-                        event::WindowEvent::MouseInput {
+                    event_handler(event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::MouseInput {
                             device_id: event::DeviceId(DeviceId),
                             state,
                             button,
                         },
-                    );
+                    });
                 }
             },
             EventOption::Scroll(ScrollEvent { x, y }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::MouseWheel {
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::MouseWheel {
                         device_id: event::DeviceId(DeviceId),
                         delta: event::MouseScrollDelta::LineDelta(x as f32, y as f32),
                         phase: event::TouchPhase::Moved,
                     },
-                );
+                });
             },
             EventOption::Quit(QuitEvent {}) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::CloseRequested,
-                );
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::CloseRequested,
+                });
             },
             EventOption::Focus(FocusEvent { focused }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::Focused(focused),
-                );
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::Focused(focused),
+                });
             },
             EventOption::Move(MoveEvent { x, y }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::Moved((x, y).into()),
-                );
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::Moved((x, y).into()),
+                });
             },
             EventOption::Resize(ResizeEvent { width, height }) => {
-                app.window_event(
-                    window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::Resized((width, height).into()),
-                );
+                event_handler(event::Event::WindowEvent {
+                    window_id: RootWindowId(window_id),
+                    event: event::WindowEvent::Resized((width, height).into()),
+                });
 
                 // Acknowledge resize after event loop.
                 event_state.resize_opt = Some((width, height));
             },
             // TODO: Screen, Clipboard, Drop
             EventOption::Hover(HoverEvent { entered }) => {
-                let event = if entered {
-                    event::WindowEvent::CursorEntered { device_id: event::DeviceId(DeviceId) }
+                if entered {
+                    event_handler(event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::CursorEntered {
+                            device_id: event::DeviceId(DeviceId),
+                        },
+                    });
                 } else {
-                    event::WindowEvent::CursorLeft { device_id: event::DeviceId(DeviceId) }
-                };
-
-                app.window_event(window_target, RootWindowId(window_id), event);
+                    event_handler(event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::CursorLeft {
+                            device_id: event::DeviceId(DeviceId),
+                        },
+                    });
+                }
             },
             other => {
                 tracing::warn!("unhandled event: {:?}", other);
@@ -500,13 +497,22 @@ impl<T: 'static> EventLoop<T> {
         }
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
+    pub fn run<F>(mut self, mut event_handler_inner: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(event::Event<T>, &event_loop::ActiveEventLoop),
+    {
+        let mut event_handler =
+            move |event: event::Event<T>, window_target: &event_loop::ActiveEventLoop| {
+                event_handler_inner(event, window_target);
+            };
+
         let mut start_cause = StartCause::Init;
+
         loop {
-            app.new_events(&self.window_target, start_cause);
+            event_handler(event::Event::NewEvents(start_cause), &self.window_target);
 
             if start_cause == StartCause::Init {
-                app.resumed(&self.window_target);
+                event_handler(event::Event::Resumed, &self.window_target);
             }
 
             // Handle window creates.
@@ -522,15 +528,23 @@ impl<T: 'static> EventLoop<T> {
 
                 self.windows.push((window, EventState::default()));
 
-                let window_id = RootWindowId(window_id);
-
                 // Send resize event on create to indicate first size.
-                let event = event::WindowEvent::Resized((properties.w, properties.h).into());
-                app.window_event(&self.window_target, window_id, event);
+                event_handler(
+                    event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::Resized((properties.w, properties.h).into()),
+                    },
+                    &self.window_target,
+                );
 
-                // Send moved event on create to indicate first position.
-                let event = event::WindowEvent::Moved((properties.x, properties.y).into());
-                app.window_event(&self.window_target, window_id, event);
+                // Send resize event on create to indicate first position.
+                event_handler(
+                    event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::Moved((properties.x, properties.y).into()),
+                    },
+                    &self.window_target,
+                );
             }
 
             // Handle window destroys.
@@ -538,8 +552,14 @@ impl<T: 'static> EventLoop<T> {
                 let mut destroys = self.window_target.p.destroys.lock().unwrap();
                 destroys.pop_front()
             } {
-                let window_id = RootWindowId(destroy_id);
-                app.window_event(&self.window_target, window_id, event::WindowEvent::Destroyed);
+                event_handler(
+                    event::Event::WindowEvent {
+                        window_id: RootWindowId(destroy_id),
+                        event: event::WindowEvent::Destroyed,
+                    },
+                    &self.window_target,
+                );
+
                 self.windows.retain(|(window, _event_state)| window.fd as u64 != destroy_id.fd);
             }
 
@@ -566,8 +586,7 @@ impl<T: 'static> EventLoop<T> {
                         window_id,
                         orbital_event.to_option(),
                         event_state,
-                        &self.window_target,
-                        app,
+                        |event| event_handler(event, &self.window_target),
                     );
                 }
 
@@ -595,7 +614,7 @@ impl<T: 'static> EventLoop<T> {
             }
 
             while let Ok(event) = self.user_events_receiver.try_recv() {
-                app.user_event(&self.window_target, event);
+                event_handler(event::Event::UserEvent(event), &self.window_target);
             }
 
             // To avoid deadlocks the redraws lock is not held during event processing.
@@ -603,14 +622,16 @@ impl<T: 'static> EventLoop<T> {
                 let mut redraws = self.window_target.p.redraws.lock().unwrap();
                 redraws.pop_front()
             } {
-                app.window_event(
+                event_handler(
+                    event::Event::WindowEvent {
+                        window_id: RootWindowId(window_id),
+                        event: event::WindowEvent::RedrawRequested,
+                    },
                     &self.window_target,
-                    RootWindowId(window_id),
-                    event::WindowEvent::RedrawRequested,
                 );
             }
 
-            app.about_to_wait(&self.window_target);
+            event_handler(event::Event::AboutToWait, &self.window_target);
 
             if self.window_target.p.exiting() {
                 break;
@@ -674,7 +695,7 @@ impl<T: 'static> EventLoop<T> {
             }
         }
 
-        app.exiting(&self.window_target);
+        event_handler(event::Event::LoopExiting, &self.window_target);
 
         Ok(())
     }

src/platform_impl/orbital/mod.rs

@@ -103,7 +103,7 @@ pub struct WindowId {
 
 impl WindowId {
     pub const fn dummy() -> Self {
-        WindowId { fd: u64::max_value() }
+        WindowId { fd: u64::MAX }
     }
 }
 

src/platform_impl/web/async/dispatcher.rs

@@ -68,7 +68,12 @@ impl<T> Dispatcher<T> {
             // SAFETY: The `transmute` is necessary because `Closure` requires `'static`. This is
             // safe because this function won't return until `f` has finished executing. See
             // `Self::new()`.
-            let closure = Closure(unsafe { std::mem::transmute(closure) });
+            let closure = Closure(unsafe {
+                std::mem::transmute::<
+                    Box<dyn FnOnce(&T) + Send>,
+                    Box<dyn FnOnce(&T) + Send + 'static>,
+                >(closure)
+            });
 
             self.0.send(closure);
 

src/platform_impl/web/async/waker.rs

@@ -1,4 +1,5 @@
 use std::future;
+use std::num::NonZeroUsize;
 use std::sync::atomic::{AtomicBool, AtomicUsize, Ordering};
 use std::sync::Arc;
 use std::task::Poll;
@@ -6,13 +7,13 @@ use std::task::Poll;
 use super::super::main_thread::MainThreadMarker;
 use super::{AtomicWaker, Wrapper};
 
-pub struct WakerSpawner<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
+pub struct WakerSpawner<T: 'static>(Wrapper<Handler<T>, Sender, NonZeroUsize>);
 
-pub struct Waker<T: 'static>(Wrapper<Handler<T>, Sender, usize>);
+pub struct Waker<T: 'static>(Wrapper<Handler<T>, Sender, NonZeroUsize>);
 
 struct Handler<T> {
     value: T,
-    handler: fn(&T, usize),
+    handler: fn(&T, NonZeroUsize, bool),
 }
 
 #[derive(Clone)]
@@ -20,7 +21,11 @@ struct Sender(Arc<Inner>);
 
 impl<T> WakerSpawner<T> {
     #[track_caller]
-    pub fn new(main_thread: MainThreadMarker, value: T, handler: fn(&T, usize)) -> Option<Self> {
+    pub fn new(
+        main_thread: MainThreadMarker,
+        value: T,
+        handler: fn(&T, NonZeroUsize, bool),
+    ) -> Option<Self> {
         let inner = Arc::new(Inner {
             counter: AtomicUsize::new(0),
             waker: AtomicWaker::new(),
@@ -37,7 +42,7 @@ impl<T> WakerSpawner<T> {
             |handler, count| {
                 let handler = handler.borrow();
                 let handler = handler.as_ref().unwrap();
-                (handler.handler)(&handler.value, count);
+                (handler.handler)(&handler.value, count, true);
             },
             {
                 let inner = Arc::clone(&inner);
@@ -46,29 +51,31 @@ impl<T> WakerSpawner<T> {
                     while let Some(count) = future::poll_fn(|cx| {
                         let count = inner.counter.swap(0, Ordering::Relaxed);
 
-                        if count > 0 {
-                            Poll::Ready(Some(count))
-                        } else {
-                            inner.waker.register(cx.waker());
+                        match NonZeroUsize::new(count) {
+                            Some(count) => Poll::Ready(Some(count)),
+                            None => {
+                                inner.waker.register(cx.waker());
 
-                            let count = inner.counter.swap(0, Ordering::Relaxed);
+                                let count = inner.counter.swap(0, Ordering::Relaxed);
 
-                            if count > 0 {
-                                Poll::Ready(Some(count))
-                            } else {
-                                if inner.closed.load(Ordering::Relaxed) {
-                                    return Poll::Ready(None);
+                                match NonZeroUsize::new(count) {
+                                    Some(count) => Poll::Ready(Some(count)),
+                                    None => {
+                                        if inner.closed.load(Ordering::Relaxed) {
+                                            return Poll::Ready(None);
+                                        }
+
+                                        Poll::Pending
+                                    },
                                 }
-
-                                Poll::Pending
-                            }
+                            },
                         }
                     })
                     .await
                     {
                         let handler = handler.borrow();
                         let handler = handler.as_ref().unwrap();
-                        (handler.handler)(&handler.value, count);
+                        (handler.handler)(&handler.value, count, false);
                     }
                 }
             },
@@ -107,7 +114,7 @@ impl<T> Drop for WakerSpawner<T> {
 
 impl<T> Waker<T> {
     pub fn wake(&self) {
-        self.0.send(1)
+        self.0.send(NonZeroUsize::MIN)
     }
 }
 

src/platform_impl/web/cursor.rs

@@ -324,7 +324,11 @@ impl Inner {
             match &self.cursor {
                 SelectedCursor::Icon(icon)
                 | SelectedCursor::Loading { previous: Previous::Icon(icon), .. } => {
-                    self.style.set("cursor", icon.name())
+                    if let CursorIcon::Default = icon {
+                        self.style.remove("cursor")
+                    } else {
+                        self.style.set("cursor", icon.name())
+                    }
                 },
                 SelectedCursor::Loading { previous: Previous::Image(cursor), .. }
                 | SelectedCursor::Image(cursor) => {

src/platform_impl/web/event_loop/mod.rs

@@ -1,10 +1,10 @@
 use std::marker::PhantomData;
 use std::sync::mpsc::{self, Receiver, Sender};
 
-use crate::application::ApplicationHandler;
 use crate::error::EventLoopError;
 use crate::event::Event;
 use crate::event_loop::ActiveEventLoop as RootActiveEventLoop;
+use crate::platform::web::{ActiveEventLoopExtWebSys, PollStrategy, WaitUntilStrategy};
 
 use super::{backend, device, window};
 
@@ -32,17 +32,33 @@ impl<T> EventLoop<T> {
         Ok(EventLoop { elw, user_event_sender, user_event_receiver })
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(self, app: &mut A) -> ! {
+    pub fn run<F>(self, mut event_handler: F) -> !
+    where
+        F: FnMut(Event<T>, &RootActiveEventLoop),
+    {
         let target = RootActiveEventLoop { p: self.elw.p.clone(), _marker: PhantomData };
 
         // SAFETY: Don't use `move` to make sure we leak the `event_handler` and `target`.
-        let handler: Box<dyn FnMut(Event<()>)> =
-            Box::new(|event| handle_event(app, &target, &self.user_event_receiver, event));
-
+        let handler: Box<dyn FnMut(Event<()>)> = Box::new(|event| {
+            let event = match event.map_nonuser_event() {
+                Ok(event) => event,
+                Err(Event::UserEvent(())) => Event::UserEvent(
+                    self.user_event_receiver
+                        .try_recv()
+                        .expect("handler woken up without user event"),
+                ),
+                Err(_) => unreachable!(),
+            };
+            event_handler(event, &target)
+        });
         // SAFETY: The `transmute` is necessary because `run()` requires `'static`. This is safe
         // because this function will never return and all resources not cleaned up by the point we
         // `throw` will leak, making this actually `'static`.
-        let handler = unsafe { std::mem::transmute(handler) };
+        let handler = unsafe {
+            std::mem::transmute::<Box<dyn FnMut(Event<()>)>, Box<dyn FnMut(Event<()>) + 'static>>(
+                handler,
+            )
+        };
         self.elw.p.run(handler, false);
 
         // Throw an exception to break out of Rust execution and use unreachable to tell the
@@ -54,12 +70,24 @@ impl<T> EventLoop<T> {
         unreachable!();
     }
 
-    pub fn spawn_app<A: ApplicationHandler<T> + 'static>(self, mut app: A) {
+    pub fn spawn<F>(self, mut event_handler: F)
+    where
+        F: 'static + FnMut(Event<T>, &RootActiveEventLoop),
+    {
         let target = RootActiveEventLoop { p: self.elw.p.clone(), _marker: PhantomData };
 
         self.elw.p.run(
             Box::new(move |event| {
-                handle_event(&mut app, &target, &self.user_event_receiver, event)
+                let event = match event.map_nonuser_event() {
+                    Ok(event) => event,
+                    Err(Event::UserEvent(())) => Event::UserEvent(
+                        self.user_event_receiver
+                            .try_recv()
+                            .expect("handler woken up without user event"),
+                    ),
+                    Err(_) => unreachable!(),
+                };
+                event_handler(event, &target)
             }),
             true,
         );
@@ -72,27 +100,20 @@ impl<T> EventLoop<T> {
     pub fn window_target(&self) -> &RootActiveEventLoop {
         &self.elw
     }
-}
 
-fn handle_event<T: 'static, A: ApplicationHandler<T>>(
-    app: &mut A,
-    target: &RootActiveEventLoop,
-    user_event_receiver: &Receiver<T>,
-    event: Event<()>,
-) {
-    match event {
-        Event::NewEvents(cause) => app.new_events(target, cause),
-        Event::WindowEvent { window_id, event } => app.window_event(target, window_id, event),
-        Event::DeviceEvent { device_id, event } => app.device_event(target, device_id, event),
-        Event::UserEvent(_) => {
-            let event =
-                user_event_receiver.try_recv().expect("user event signaled but not received");
-            app.user_event(target, event);
-        },
-        Event::Suspended => app.suspended(target),
-        Event::Resumed => app.resumed(target),
-        Event::AboutToWait => app.about_to_wait(target),
-        Event::LoopExiting => app.exiting(target),
-        Event::MemoryWarning => app.memory_warning(target),
+    pub fn set_poll_strategy(&self, strategy: PollStrategy) {
+        self.elw.set_poll_strategy(strategy);
+    }
+
+    pub fn poll_strategy(&self) -> PollStrategy {
+        self.elw.poll_strategy()
+    }
+
+    pub fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.elw.set_wait_until_strategy(strategy);
+    }
+
+    pub fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.elw.wait_until_strategy()
     }
 }

src/platform_impl/web/event_loop/runner.rs

@@ -8,18 +8,21 @@ use crate::event::{
     WindowEvent,
 };
 use crate::event_loop::{ControlFlow, DeviceEvents};
-use crate::platform::web::PollStrategy;
+use crate::platform::web::{PollStrategy, WaitUntilStrategy};
 use crate::platform_impl::platform::backend::EventListenerHandle;
 use crate::platform_impl::platform::r#async::{DispatchRunner, Waker, WakerSpawner};
 use crate::platform_impl::platform::window::Inner;
 use crate::window::WindowId;
 
+use js_sys::Function;
 use std::cell::{Cell, RefCell};
 use std::collections::{HashSet, VecDeque};
 use std::iter;
+use std::num::NonZeroUsize;
 use std::ops::Deref;
 use std::rc::{Rc, Weak};
-use wasm_bindgen::prelude::Closure;
+use wasm_bindgen::prelude::{wasm_bindgen, Closure};
+use wasm_bindgen::JsCast;
 use web_sys::{Document, KeyboardEvent, PageTransitionEvent, PointerEvent, WheelEvent};
 use web_time::{Duration, Instant};
 
@@ -40,6 +43,7 @@ pub struct Execution {
     proxy_spawner: WakerSpawner<Weak<Self>>,
     control_flow: Cell<ControlFlow>,
     poll_strategy: Cell<PollStrategy>,
+    wait_until_strategy: Cell<WaitUntilStrategy>,
     exit: Cell<bool>,
     runner: RefCell<RunnerEnum>,
     suspended: Cell<bool>,
@@ -133,18 +137,20 @@ impl Shared {
         let document = window.document().expect("Failed to obtain document");
 
         Shared(Rc::<Execution>::new_cyclic(|weak| {
-            let proxy_spawner = WakerSpawner::new(main_thread, weak.clone(), |runner, count| {
-                if let Some(runner) = runner.upgrade() {
-                    Shared(runner).send_events(iter::repeat(Event::UserEvent(())).take(count))
-                }
-            })
-            .expect("`EventLoop` has to be created in the main thread");
+            let proxy_spawner =
+                WakerSpawner::new(main_thread, weak.clone(), |runner, count, local| {
+                    if let Some(runner) = runner.upgrade() {
+                        Shared(runner).send_user_events(count, local)
+                    }
+                })
+                .expect("`EventLoop` has to be created in the main thread");
 
             Execution {
                 main_thread,
                 proxy_spawner,
                 control_flow: Cell::new(ControlFlow::default()),
                 poll_strategy: Cell::new(PollStrategy::default()),
+                wait_until_strategy: Cell::new(WaitUntilStrategy::default()),
                 exit: Cell::new(false),
                 runner: RefCell::new(RunnerEnum::Pending),
                 suspended: Cell::new(false),
@@ -460,6 +466,51 @@ impl Shared {
         self.send_events(iter::once(event));
     }
 
+    // Add a series of user events to the event loop runner
+    //
+    // This will schedule the event loop to wake up instead of waking it up immediately if its not
+    // running.
+    pub(crate) fn send_user_events(&self, count: NonZeroUsize, local: bool) {
+        // If the event loop is closed, it should discard any new events
+        if self.is_closed() {
+            return;
+        }
+
+        if local {
+            // If the loop is not running and triggered locally, queue on next microtick.
+            if let Ok(RunnerEnum::Running(ref runner)) =
+                self.0.runner.try_borrow().as_ref().map(Deref::deref)
+            {
+                // If we're currently polling let `send_events` do its job.
+                if !matches!(runner.state, State::Poll { .. }) {
+                    #[wasm_bindgen]
+                    extern "C" {
+                        #[wasm_bindgen(js_name = queueMicrotask)]
+                        fn queue_microtask(task: Function);
+                    }
+
+                    queue_microtask(
+                        Closure::once_into_js({
+                            let this = Rc::downgrade(&self.0);
+                            move || {
+                                if let Some(shared) = this.upgrade() {
+                                    Shared(shared).send_events(
+                                        iter::repeat(Event::UserEvent(())).take(count.get()),
+                                    )
+                                }
+                            }
+                        })
+                        .unchecked_into(),
+                    );
+
+                    return;
+                }
+            }
+        }
+
+        self.send_events(iter::repeat(Event::UserEvent(())).take(count.get()))
+    }
+
     // Add a series of events to the event loop runner
     //
     // It will determine if the event should be immediately sent to the user or buffered for later
@@ -473,7 +524,7 @@ impl Shared {
         match self.0.runner.try_borrow().as_ref().map(Deref::deref) {
             Ok(RunnerEnum::Running(ref runner)) => {
                 // If we're currently polling, queue this and wait for the poll() method to be
-                // called
+                // called.
                 if let State::Poll { .. } = runner.state {
                     process_immediately = false;
                 }
@@ -647,6 +698,7 @@ impl Shared {
                         start,
                         end,
                         _timeout: backend::Schedule::new_with_duration(
+                            self.wait_until_strategy(),
                             self.window(),
                             move || cloned.resume_time_reached(start, end),
                             delay,
@@ -759,6 +811,14 @@ impl Shared {
         self.0.poll_strategy.get()
     }
 
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.0.wait_until_strategy.set(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.0.wait_until_strategy.get()
+    }
+
     pub(crate) fn waker(&self) -> Waker<Weak<Execution>> {
         self.0.proxy_spawner.waker()
     }

src/platform_impl/web/event_loop/window_target.rs

@@ -18,7 +18,7 @@ use crate::event::{
 };
 use crate::event_loop::{ControlFlow, DeviceEvents};
 use crate::keyboard::ModifiersState;
-use crate::platform::web::{CustomCursorFuture, PollStrategy};
+use crate::platform::web::{CustomCursorFuture, PollStrategy, WaitUntilStrategy};
 use crate::platform_impl::platform::cursor::CustomCursor;
 use crate::platform_impl::platform::r#async::Waker;
 use crate::window::{
@@ -682,6 +682,14 @@ impl ActiveEventLoop {
         self.runner.poll_strategy()
     }
 
+    pub(crate) fn set_wait_until_strategy(&self, strategy: WaitUntilStrategy) {
+        self.runner.set_wait_until_strategy(strategy)
+    }
+
+    pub(crate) fn wait_until_strategy(&self) -> WaitUntilStrategy {
+        self.runner.wait_until_strategy()
+    }
+
     pub(crate) fn waker(&self) -> Waker<Weak<Execution>> {
         self.runner.waker()
     }

src/platform_impl/web/web_sys/canvas.rs

@@ -427,8 +427,8 @@ impl Canvas {
 
     pub(crate) fn on_resize_scale<S, R>(&mut self, scale_handler: S, size_handler: R)
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
         self.on_resize_scale = Some(ResizeScaleHandle::new(
             self.window().clone(),

src/platform_impl/web/web_sys/resize_scaling.rs

@@ -16,7 +16,7 @@ use super::media_query_handle::MediaQueryListHandle;
 use std::cell::{Cell, RefCell};
 use std::rc::Rc;
 
-pub struct ResizeScaleHandle(Rc<RefCell<ResizeScaleInternal>>);
+pub struct ResizeScaleHandle(Rc<ResizeScaleInternal>);
 
 impl ResizeScaleHandle {
     pub(crate) fn new<S, R>(
@@ -28,8 +28,8 @@ impl ResizeScaleHandle {
         resize_handler: R,
     ) -> Self
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
         Self(ResizeScaleInternal::new(
             window,
@@ -42,7 +42,7 @@ impl ResizeScaleHandle {
     }
 
     pub(crate) fn notify_resize(&self) {
-        self.0.borrow_mut().notify()
+        self.0.notify()
     }
 }
 
@@ -53,11 +53,11 @@ struct ResizeScaleInternal {
     document: Document,
     canvas: HtmlCanvasElement,
     style: Style,
-    mql: MediaQueryListHandle,
+    mql: RefCell<MediaQueryListHandle>,
     observer: ResizeObserver,
     _observer_closure: Closure<dyn FnMut(Array, ResizeObserver)>,
-    scale_handler: Box<dyn FnMut(PhysicalSize<u32>, f64)>,
-    resize_handler: Box<dyn FnMut(PhysicalSize<u32>)>,
+    scale_handler: Box<dyn Fn(PhysicalSize<u32>, f64)>,
+    resize_handler: Box<dyn Fn(PhysicalSize<u32>)>,
     notify_scale: Cell<bool>,
 }
 
@@ -69,12 +69,12 @@ impl ResizeScaleInternal {
         style: Style,
         scale_handler: S,
         resize_handler: R,
-    ) -> Rc<RefCell<Self>>
+    ) -> Rc<Self>
     where
-        S: 'static + FnMut(PhysicalSize<u32>, f64),
-        R: 'static + FnMut(PhysicalSize<u32>),
+        S: 'static + Fn(PhysicalSize<u32>, f64),
+        R: 'static + Fn(PhysicalSize<u32>),
     {
-        Rc::<RefCell<ResizeScaleInternal>>::new_cyclic(|weak_self| {
+        Rc::<ResizeScaleInternal>::new_cyclic(|weak_self| {
             let mql = Self::create_mql(&window, {
                 let weak_self = weak_self.clone();
                 move |mql| {
@@ -86,9 +86,7 @@ impl ResizeScaleInternal {
 
             let weak_self = weak_self.clone();
             let observer_closure = Closure::new(move |entries: Array, _| {
-                if let Some(rc_self) = weak_self.upgrade() {
-                    let mut this = rc_self.borrow_mut();
-
+                if let Some(this) = weak_self.upgrade() {
                     let size = this.process_entry(entries);
 
                     if this.notify_scale.replace(false) {
@@ -101,18 +99,18 @@ impl ResizeScaleInternal {
             });
             let observer = Self::create_observer(&canvas, observer_closure.as_ref());
 
-            RefCell::new(Self {
+            Self {
                 window,
                 document,
                 canvas,
                 style,
-                mql,
+                mql: RefCell::new(mql),
                 observer,
                 _observer_closure: observer_closure,
                 scale_handler: Box::new(scale_handler),
                 resize_handler: Box::new(resize_handler),
                 notify_scale: Cell::new(false),
-            })
+            }
         })
     }
 
@@ -152,7 +150,7 @@ impl ResizeScaleInternal {
         observer
     }
 
-    fn notify(&mut self) {
+    fn notify(&self) {
         if !self.document.contains(Some(&self.canvas)) || self.style.get("display") == "none" {
             let size = PhysicalSize::new(0, 0);
 
@@ -200,10 +198,9 @@ impl ResizeScaleInternal {
         }
     }
 
-    fn handle_scale(this: Rc<RefCell<Self>>, mql: &MediaQueryList) {
-        let weak_self = Rc::downgrade(&this);
-        let mut this = this.borrow_mut();
-        let scale = super::scale_factor(&this.window);
+    fn handle_scale(self: Rc<Self>, mql: &MediaQueryList) {
+        let weak_self = Rc::downgrade(&self);
+        let scale = super::scale_factor(&self.window);
 
         // TODO: confirm/reproduce this problem, see:
         // <https://github.com/rust-windowing/winit/issues/2597>.
@@ -217,15 +214,15 @@ impl ResizeScaleInternal {
             return;
         }
 
-        let new_mql = Self::create_mql(&this.window, move |mql| {
+        let new_mql = Self::create_mql(&self.window, move |mql| {
             if let Some(rc_self) = weak_self.upgrade() {
                 Self::handle_scale(rc_self, mql);
             }
         });
-        this.mql = new_mql;
+        self.mql.replace(new_mql);
 
-        this.notify_scale.set(true);
-        this.notify();
+        self.notify_scale.set(true);
+        self.notify();
     }
 
     fn process_entry(&self, entries: Array) -> PhysicalSize<u32> {

src/platform_impl/web/web_sys/schedule.rs

@@ -1,12 +1,14 @@
-use js_sys::{Function, Object, Promise, Reflect};
+use js_sys::{Array, Function, Object, Promise, Reflect};
 use std::cell::OnceCell;
 use std::time::Duration;
 use wasm_bindgen::closure::Closure;
 use wasm_bindgen::prelude::wasm_bindgen;
 use wasm_bindgen::{JsCast, JsValue};
-use web_sys::{AbortController, AbortSignal, MessageChannel, MessagePort};
+use web_sys::{
+    AbortController, AbortSignal, Blob, BlobPropertyBag, MessageChannel, MessagePort, Url, Worker,
+};
 
-use crate::platform::web::PollStrategy;
+use crate::platform::web::{PollStrategy, WaitUntilStrategy};
 
 #[derive(Debug)]
 pub struct Schedule {
@@ -29,6 +31,7 @@ enum Inner {
         port: MessagePort,
         _timeout_closure: Closure<dyn FnMut()>,
     },
+    Worker(MessagePort),
 }
 
 impl Schedule {
@@ -45,14 +48,24 @@ impl Schedule {
         }
     }
 
-    pub fn new_with_duration<F>(window: &web_sys::Window, f: F, duration: Duration) -> Schedule
+    pub fn new_with_duration<F>(
+        strategy: WaitUntilStrategy,
+        window: &web_sys::Window,
+        f: F,
+        duration: Duration,
+    ) -> Schedule
     where
         F: 'static + FnMut(),
     {
-        if has_scheduler_support(window) {
-            Self::new_scheduler(window, f, Some(duration))
-        } else {
-            Self::new_timeout(window.clone(), f, Some(duration))
+        match strategy {
+            WaitUntilStrategy::Scheduler => {
+                if has_scheduler_support(window) {
+                    Self::new_scheduler(window, f, Some(duration))
+                } else {
+                    Self::new_timeout(window.clone(), f, Some(duration))
+                }
+            },
+            WaitUntilStrategy::Worker => Self::new_worker(f, duration),
         }
     }
 
@@ -153,6 +166,44 @@ impl Schedule {
             },
         }
     }
+
+    fn new_worker<F>(f: F, duration: Duration) -> Schedule
+    where
+        F: 'static + FnMut(),
+    {
+        thread_local! {
+            static URL: ScriptUrl = ScriptUrl::new(include_str!("worker.min.js"));
+            static WORKER: Worker = URL.with(|url| Worker::new(&url.0)).expect("`new Worker()` is not expected to fail with a local script");
+        }
+
+        let channel = MessageChannel::new().unwrap();
+        let closure = Closure::new(f);
+        let port_1 = channel.port1();
+        port_1.set_onmessage(Some(closure.as_ref().unchecked_ref()));
+        port_1.start();
+
+        // `Duration::as_millis()` always rounds down (because of truncation), we want to round
+        // up instead. This makes sure that the we never wake up **before** the given time.
+        let duration = duration
+            .as_secs()
+            .try_into()
+            .ok()
+            .and_then(|secs: u32| secs.checked_mul(1000))
+            .and_then(|secs| secs.checked_add(duration_millis_ceil(duration)))
+            .unwrap_or(u32::MAX);
+
+        WORKER
+            .with(|worker| {
+                let port_2 = channel.port2();
+                worker.post_message_with_transfer(
+                    &Array::of2(&port_2, &duration.into()),
+                    &Array::of1(&port_2).into(),
+                )
+            })
+            .expect("`Worker.postMessage()` is not expected to fail");
+
+        Schedule { _closure: closure, inner: Inner::Worker(port_1) }
+    }
 }
 
 impl Drop for Schedule {
@@ -165,6 +216,10 @@ impl Drop for Schedule {
                 port.close();
                 port.set_onmessage(None);
             },
+            Inner::Worker(port) => {
+                port.close();
+                port.set_onmessage(None);
+            },
         }
     }
 }
@@ -226,6 +281,29 @@ fn has_idle_callback_support(window: &web_sys::Window) -> bool {
     })
 }
 
+struct ScriptUrl(String);
+
+impl ScriptUrl {
+    fn new(script: &str) -> Self {
+        let sequence = Array::of1(&script.into());
+        let mut property = BlobPropertyBag::new();
+        property.type_("text/javascript");
+        let blob = Blob::new_with_str_sequence_and_options(&sequence, &property)
+            .expect("`new Blob()` should never throw");
+
+        let url = Url::create_object_url_with_blob(&blob)
+            .expect("`URL.createObjectURL()` should never throw");
+
+        Self(url)
+    }
+}
+
+impl Drop for ScriptUrl {
+    fn drop(&mut self) {
+        Url::revoke_object_url(&self.0).expect("`URL.revokeObjectURL()` should never throw");
+    }
+}
+
 #[wasm_bindgen]
 extern "C" {
     type WindowSupportExt;

src/platform_impl/web/web_sys/worker.js

@@ -0,0 +1,10 @@
+onmessage = event => {
+    const [port, timeout] = event.data
+    const f = () => port.postMessage(undefined)
+
+    if ('scheduler' in this) {
+        scheduler.postTask(f, { delay: timeout })
+    } else {
+        setTimeout(f, timeout)
+    }
+}

src/platform_impl/web/web_sys/worker.min.js

@@ -0,0 +1 @@
+onmessage=e=>{let[s,t]=e.data,a=()=>s.postMessage(void 0);"scheduler"in this?scheduler.postTask(a,{delay:t}):setTimeout(a,t)};

src/platform_impl/windows/event_loop.rs

@@ -57,7 +57,6 @@ use windows_sys::Win32::UI::WindowsAndMessaging::{
     WS_EX_NOACTIVATE, WS_EX_TOOLWINDOW, WS_EX_TRANSPARENT, WS_OVERLAPPED, WS_POPUP, WS_VISIBLE,
 };
 
-use crate::application::ApplicationHandler;
 use crate::dpi::{PhysicalPosition, PhysicalSize};
 use crate::error::EventLoopError;
 use crate::event::{
@@ -216,14 +215,17 @@ impl<T: 'static> EventLoop<T> {
         &self.window_target
     }
 
-    pub fn run_app<A: ApplicationHandler<T>>(mut self, app: &mut A) -> Result<(), EventLoopError> {
-        self.run_app_on_demand(app)
+    pub fn run<F>(mut self, event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
+        self.run_on_demand(event_handler)
     }
 
-    pub fn run_app_on_demand<A: ApplicationHandler<T>>(
-        &mut self,
-        app: &mut A,
-    ) -> Result<(), EventLoopError> {
+    pub fn run_on_demand<F>(&mut self, mut event_handler: F) -> Result<(), EventLoopError>
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         {
             let runner = &self.window_target.p.runner_shared;
 
@@ -234,32 +236,21 @@ impl<T: 'static> EventLoop<T> {
             // returning
             unsafe {
                 runner.set_event_handler(move |event| {
-                    match event {
-                        Event::NewEvents(cause) => app.new_events(event_loop_windows_ref, cause),
-                        Event::WindowEvent { window_id, event } => {
-                            app.window_event(event_loop_windows_ref, window_id, event)
-                        },
-                        Event::DeviceEvent { device_id, event } => {
-                            app.device_event(event_loop_windows_ref, device_id, event)
-                        },
-                        // The shared `EventLoopRunner` is not parameterized
-                        // `EventLoopProxy::send_event()` calls `PostMessage`
-                        // to wakeup and dispatch a placeholder `UserEvent`,
-                        // when we received the placeholder event here, the
-                        // real UserEvent(T) should already be put in the
-                        // mpsc channel and ready to be pulled
-                        Event::UserEvent(_) => {
-                            let event = user_event_receiver
+                    // the shared `EventLoopRunner` is not parameterized
+                    // `EventLoopProxy::send_event()` calls `PostMessage`
+                    // to wakeup and dispatch a placeholder `UserEvent`,
+                    // when we received the placeholder event here, the
+                    // real UserEvent(T) should already be put in the
+                    // mpsc channel and ready to be pulled
+                    let event = match event.map_nonuser_event() {
+                        Ok(non_user_event) => non_user_event,
+                        Err(_user_event_placeholder) => Event::UserEvent(
+                            user_event_receiver
                                 .try_recv()
-                                .expect("user event signaled but not received");
-                            app.user_event(event_loop_windows_ref, event);
-                        },
-                        Event::Suspended => app.suspended(event_loop_windows_ref),
-                        Event::Resumed => app.resumed(event_loop_windows_ref),
-                        Event::AboutToWait => app.about_to_wait(event_loop_windows_ref),
-                        Event::LoopExiting => app.exiting(event_loop_windows_ref),
-                        Event::MemoryWarning => app.memory_warning(event_loop_windows_ref),
-                    }
+                                .expect("user event signaled but not received"),
+                        ),
+                    };
+                    event_handler(event, event_loop_windows_ref)
                 });
             }
         }
@@ -293,11 +284,10 @@ impl<T: 'static> EventLoop<T> {
         }
     }
 
-    pub fn pump_app_events<A: ApplicationHandler<T>>(
-        &mut self,
-        timeout: Option<Duration>,
-        app: &mut A,
-    ) -> PumpStatus {
+    pub fn pump_events<F>(&mut self, timeout: Option<Duration>, mut event_handler: F) -> PumpStatus
+    where
+        F: FnMut(Event<T>, &RootAEL),
+    {
         {
             let runner = &self.window_target.p.runner_shared;
             let event_loop_windows_ref = &self.window_target;
@@ -312,34 +302,16 @@ impl<T: 'static> EventLoop<T> {
             // event handler.
             unsafe {
                 runner.set_event_handler(move |event| {
-                    match event {
-                        Event::NewEvents(cause) => app.new_events(event_loop_windows_ref, cause),
-                        Event::WindowEvent { window_id, event } => {
-                            app.window_event(event_loop_windows_ref, window_id, event)
-                        },
-                        Event::DeviceEvent { device_id, event } => {
-                            app.device_event(event_loop_windows_ref, device_id, event)
-                        },
-                        // The shared `EventLoopRunner` is not parameterized
-                        // `EventLoopProxy::send_event()` calls `PostMessage`
-                        // to wakeup and dispatch a placeholder `UserEvent`,
-                        // when we received the placeholder event here, the
-                        // real UserEvent(T) should already be put in the
-                        // mpsc channel and ready to be pulled
-                        Event::UserEvent(_) => {
-                            let event = user_event_receiver
-                                .try_recv()
-                                .expect("user event signaled but not received");
-                            app.user_event(event_loop_windows_ref, event);
-                        },
-                        Event::Suspended => app.suspended(event_loop_windows_ref),
-                        Event::Resumed => app.resumed(event_loop_windows_ref),
-                        Event::AboutToWait => app.about_to_wait(event_loop_windows_ref),
-                        Event::LoopExiting => app.exiting(event_loop_windows_ref),
-                        Event::MemoryWarning => app.memory_warning(event_loop_windows_ref),
-                    }
+                    let event = match event.map_nonuser_event() {
+                        Ok(non_user_event) => non_user_event,
+                        Err(_user_event_placeholder) => Event::UserEvent(
+                            user_event_receiver
+                                .recv()
+                                .expect("user event signaled but not received"),
+                        ),
+                    };
+                    event_handler(event, event_loop_windows_ref)
                 });
-
                 runner.wakeup();
             }
         }

src/platform_impl/windows/mod.rs

@@ -1,5 +1,3 @@
-#![cfg(windows_platform)]
-
 use smol_str::SmolStr;
 use windows_sys::Win32::Foundation::{HANDLE, HWND};
 use windows_sys::Win32::UI::WindowsAndMessaging::{HMENU, WINDOW_LONG_PTR_INDEX};

src/window.rs

@@ -393,7 +393,6 @@ impl WindowAttributes {
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
     /// - **Wayland:** This controls only CSD. When using `None` it'll try to use dbus to get the
     ///   system preference. When explicit theme is used, this will avoid dbus all together.
     /// - **x11:** Build window with `_GTK_THEME_VARIANT` hint set to `dark` or `light`.
@@ -632,7 +631,8 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// **Wayland:** - schedules a frame callback to throttle [`WindowEvent::RedrawRequested`].
+    /// - **Android / iOS / X11 / Web / Windows / macOS / Orbital:** Unsupported.
+    /// - **Wayland:** Schedules a frame callback to throttle [`WindowEvent::RedrawRequested`].
     ///
     /// [`WindowEvent::RedrawRequested`]: crate::event::WindowEvent::RedrawRequested
     #[inline]
@@ -941,8 +941,7 @@ impl Window {
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** If you're not drawing to the window yourself, you might have to set the
-    ///   background color of the window to enable transparency.
+    /// - **macOS:** This will reset the window's background color.
     /// - **Web / iOS / Android:** Unsupported.
     /// - **X11:** Can only be set while building the window, with
     ///   [`WindowAttributes::with_transparent`].
@@ -1354,11 +1353,12 @@ impl Window {
         self.window.maybe_queue_on_main(move |w| w.request_user_attention(request_type))
     }
 
-    /// Sets the current window theme. Use `None` to fallback to system default.
+    /// Set or override the window theme.
+    ///
+    /// Specify `None` to reset the theme to the system default.
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
     /// - **Wayland:** Sets the theme for the client side decorations. Using `None` will use dbus to
     ///   get the system preference.
     /// - **X11:** Sets `_GTK_THEME_VARIANT` hint to `dark` or `light` and if `None` is used, it
@@ -1374,12 +1374,14 @@ impl Window {
         self.window.maybe_queue_on_main(move |w| w.set_theme(theme))
     }
 
-    /// Returns the current window theme.
+    /// Returns the current window theme override.
+    ///
+    /// Returns `None` if the current theme is set as the system default, or if it cannot be
+    /// determined on the current platform.
     ///
     /// ## Platform-specific
     ///
-    /// - **macOS:** This is an app-wide setting.
-    /// - **iOS / Android / Wayland / x11 / Orbital:** Unsupported.
+    /// - **iOS / Android / Wayland / x11 / Orbital:** Unsupported, returns `None`.
     #[inline]
     pub fn theme(&self) -> Option<Theme> {
         let _span = tracing::debug_span!("winit::Window::theme",).entered();